Charophytes from the Pozo D-129 Formation (lower Aptian, Lower Cretaceous), source rock in the Golfo San Jorge Basin, Patagonia, Argentina Andrea De Sosa Tomas a, * , Carles Martín-Closas b, c , Patricia Vallati a a Laboratorio de Biostratigrafía “Dr. Eduardo Musacchio”, Departamento de Geología, Universidad Nacional de la Patagonia San Juan Bosco, Ciudad, Universitaria Km. 4, Comodoro Rivadavia, Chubut, 9000, Argentina b Departament de Din amica de la Terra i de l'Oce a, Facultat de Ci encies de la Terra, Universitat de Barcelona-UB, 08028, Barcelona, Catalonia, Spain c Institut de Recerca de la Biodiversitat (IRBio), Universitat de Barcelona-UB, 08028, Barcelona, Catalonia, Spain article info Article history: Received 13 March 2023 Received in revised form 13 June 2023 Accepted in revised form 4 July 2023 Available online 8 July 2023 Keywords: Charophyta Biostratigraphy Paleoecology Paleobiogeography Lower Cretaceous Chubut Group abstract The charophytes studied here are from the uppermost part of the Pozo D-129 Formation in Sierra Silva, which belongs to the Golfo San Jorge Basin. Fructifications from three charophyte species belonging to the families Characeae and Clavatoraceae are described and illustrated. Two charophyte assemblages obtained from the lower part of the section were characterized: Assemblage 1, formed exclusively of characeans, Mesochara stipitata and Lamprothamnium? barcinensis, and Assemblage 2, composed of L.? barcinensis and the clavatoraceans Clavator harrisii var. harrisii and Clavator harrisii var. zavialensis. These differences in the composition of the charophyte floras are related to different paleoecological conditions that changed from the temporary, unstable water bodies represented in the lower assemblage studied to more stable and permanent lake conditions. The charophyte assemblages together with the previously recorded palynological data suggest a late early Aptian age for the succession of the Pozo D-129 For- mation studied. Likewise, the charophytes contribute to the paleobiogeographic history of two con- spicuous taxa, M. stipitata and C. harrisii var. zavialensis, which are reported here for the first time in the Lower Cretaceous deposits of the basin. © 2023 Elsevier Ltd. All rights reserved. 1. Introduction Charophyte gyrogonites and utricles belonging to the Characeae and Clavatoraceae families respectively have been widely identified in the Lower Cretaceous deposits of Argentina (Musacchio in Hechem et al., 1987; Musacchio, 2000; De Sosa Tomas et al., 2017 , 2022). Representatives of the Clavatoraceae have been recorded in the non-marine Patagonian basins of Neuqu en, Ca~ nad on Asfalto, and Golfo San Jorge from the Barremian‒Aptian interval; they include Atopochara trivolvis triquetra Grambast, 1968, Clavator harrisii Peck, 1941 , Clavator calcitrapus jiangluoensis nov. comb. P erez-Cano et al., 2020 (¼Triclypella patagonica Musacchio, 1989), and Diectochara andica Musacchio, 1971 (Musacchio, 1971 , 1995, 2000). Palynological studies of the subsurface deposits of the Pozo D- 129 Formation led Archangelsky et al. (1984) to associate part of the unit with the Antulsporites-Clavatipollenites biozone of the Austral Basin, which is Aptian in age. Musacchio (in Hechem et al., 1987) reported an assemblage of calcareous microfossils in the Pozo D- 129 Formation containing the utricles of Flabellochara aff. harrisii (an early synonym of C. harrisii) and Stellatochara aff. mundula (synonymous with L.? barcinensis) that were associated with the ostracod Pattersoncypris, which he also attributed to the Aptian. Later, studies of a palynoflora with primitive angiosperms (Vallati, 1996, 2013) and of a calcareous microfossil assemblage (Carignano et al., 2017) in the outcrops of Sierra Silva suggested a Barremian‒Aptian interval for the deposits. A similar age (early Barremian‒Aptian) has been assigned to a palynological assem- blage from subsurface deposits reported by P erez-Loinaze et al. (2019). Based on U/Pb analyses on zircons, Allard et al. (2022) proposed an Albian age for the upper deltaic levels of the Pozo D- 129 Formation in the locality of Codo del Río Senguerr. These au- thors interpreted a diachronic boundary for the top of the unit, which would be younger south of Sierra Silva. * Corresponding author. E-mail address: adesosatomas@gmail.com (A. De Sosa Tomas). Contents lists available at ScienceDirect Cretaceous Research journal homepage: www.elsevier.com/locate/CretRes https://doi.org/10.1016/j.cretres.2023.105652 0195-6671/© 2023 Elsevier Ltd. All rights reserved. Cretaceous Research 151 (2023) 105652