A Mustersan Paleosol bearing land microgastropods (Charopidae) from the Sarmiento Formation, Eocene of Central Patagonia: Climatic implications
The lower section of Puesto Almendra Member (Sarmiento Formation) at Gran Barranca (Chubut province, Argentina), is composed of tuffs, tuffaceous paleosols and fluvial sandstones and intraformational conglomerates of latest Middle Eocene age. In the lower pink paleosol (Rosado bed) terrestrial microgastropods, bee trace fossils and mammal remains referable to Mustersan SALMA have been recovered. This paleosol occurs within a pyroclastic loess-paleosol succession, that was originated as distal ash falls on loessic plains during a low humidity period. Subsequently, the ash was calcretized through pedogenesis. The massive micritic fabric and frequent traces of Cellifornia isp. indicate semiarid conditions. The snails are the second South American fossil record of Charopidae (Gyrocochlea? sp. cf. S. mirabilis Hylton Scott, Stephadiscus sp. cf. S. lyratus (Couthouy in Gould), Zilchogyra sp. 1 and Z. sp. 2), living genera of wide geographic distribution in South America, from tropical to magellanic regions. In broad agreement with Paleogene global climatic changes, a cooling and aridity trend in Patagonia through the late Eocene would have likely occurred within a variable climate scenario, perhaps involving high frequency fluctuations. The stratigraphic last occurrences of some groups of gastropods (i.e. Strophocheilus, Megalobulimus and Paleobulimulus) may be related to these phenomena, whereas genera Gyrocochlea?, Stephadiscus and Zilchogyra may have survived in humid areas of southern Argentina and Chile.
Bellosi, ES; Miquel, SE; Kay, RF; Madden, RH
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