Submitted : April 30 th , 2020 – Accepted : July 1 6th , 2020 – Posted online : July 2 3th , 2020 To link and cite this article: doi: 10.5710/AMGH.16.07.2020.3356 1 NEW MIDDLE TRIASSIC POLLEN TAXA OF THE SAN RAFAEL BASIN, 2 MENDOZA PROVINCE, ARGENTINA 3 NUEVOS TAXONES DE POLEN TRIÁSICO MEDIO DE LA CUENCA SAN 4 RAFAEL, PROVINCIA DE MENDOZA, ARGENTINA 5 6 PEDRO R. GUTIÉRREZ1, ANA MARÍA ZAVATTIERI2 7 1Sección Paleopalinología, Área Paleontología, Museo Argentino de Ciencias Naturales 8 “B. Rivadavia”, CONICET, Av. Ángel Gallardo 470, C1405DJR Ciudad Autónoma de 9 Buenos Aires, Argentina. [email protected] 10 2Unidad de Paleopalinología, Departamento de Paleontología, Instituto Argentino de 11 Nivología, Glaciología y Ciencias Ambientales (IANIGLA), CCT-CONICET-Mendoza, 12 Av. A. Ruíz Leal s/n, Parque General San Martín, M5502IRA Mendoza, Argentina. 13 [email protected] 14 15 40 pag. (26 text + 14 references); 9 figs.; 2 tables 16 17 Proposed header: GUTIÉRREZ & ZAVATTIERI: PALYNOFLORAS FROM THE 18 LADINIAN, ARGENTINA. 19 20 Short Description: New pollen taxa are described from the Ladinian Quebrada de los 21 Fósiles Formation, Puesto Viejo Group, San Rafael Basin, Argentina. 22 23 Corresponding author: Pedro Raúl Gutiérrez. [email protected]. 1 24 25 Abstract. New pollen grains are described from diverse palynological assemblages 26 recorded from the Quebrada de los Fósiles Formation, lower unit of the Puesto Viejo 27 Group, San Rafael Basin (Mendoza, Argentina), southwestern Gondwana. Two new 28 pollen genera, Mendozapollenites and Crackipollenites are proposed, and three new 29 species, Mendozapollenites variabilis, Angustisulcites hexagonalis and Crackipollenites 30 polygonata and Crackipollenites sp. A, as well as, a monosaccate pollen indeterminate 31 (Form A) are fully described and illustrated. The microflora contains high proportions of 32 sphenopsid and lycopsid spores together with true ferns and bryophyte spores as minor 33 components; non-taeniate pteridosperm bisaccate pollen grains, taeniate monosaccate and 34 bisaccate pollen together with scarce monosulcate and inaperturate grains, among other 35 less frequent gymnosperm pollen and the co-occurrence of chlorococcalean algae and 36 fungal spores. The sedimentation of the Quebrada de los Fósiles Formation took place 37 during Middle Triassic Ladinian age, confirmed by recent radiometric data carried out 38 from both base and top effusive levels (ignimbrites) of the main profile of the unit. Thus, 39 this is the first unequivocal and unique microflora recorded at present for the Ladinian in 40 South America. 41 Key words: Palynology. Pollen grains. Systematics. Ladinian. Argentina. Southwestern 42 Gondwana. 43 Resumen. NUEVOS TAXONES DE POLEN TRIÁSICO MEDIO DE LA CUENCA 44 SAN RAFAEL, PROVINCIA DE MENDOZA, ARGENTINA. Se describen nuevos 45 granos de polen de diversas asociaciones palinológicas registradas de la Formación 46 Quebrada de los Fósiles, unidad inferior del Grupo Puesto Viejo, cuenca de San Rafael 2 47 (Mendoza, Argentina), suroeste de Gondwana. Se proponen dos nuevos géneros, 48 Mendozapollenites y Crackipollenites, se describen e ilustran las nuevas especies, 49 Mendozapollenites variabilis, Angustisulcites hexagonalis, Crackipollenites polygonata y 50 C. sp. A, y también un grano de polen monosacado indeterminado (Forma A). La 51 microflora contiene altas proporciones de esporas de esfenópsidas y licópsidas, junto con 52 esporas de helechos verdaderos y de briófitas, como componentes menores; granos de 53 polen bisacados no taeniados de pteridospermas, y granos de polen monosacados y 54 bisaccados taeniados, junto con escasos granos monosulcados e inaperturados entre otros 55 granos de pollen de gimnospermas menos frecuentes, y la co-ocurrencia de algas 56 clorococales y esporas de hongos. La sedimentación de la Formación Quebrada de los 57 Fósiles tuvo lugar durante el Triásico Medio (Ladiniano), confirmado por dataciones 58 radiométricas recientes realizadas en los niveles de ignimbritas de la base y del techo del 59 perfil tipo de la unidad. Por lo tanto, esta es la primera e inequívoca palinoflora registrada 60 hasta ahora para el Ladiniano en América del Sur. 61 Palabras clave. Palinología. Granos de polen. Sistemática. Ladiniano. Argentina. 62 Suroeste de Gondwana. 3 63 64 THE TRIASSIC CONTINENTAL DEPOSITS IN THE SAN RAFAEL BASIN (also referred as San 65 Rafael depocenter by Ottone et al., 2018 or San Rafael Block by Cariglino et al., 2019 66 and Monti & Franzese, 2016), southwest of Mendoza Province, central-west Argentina 67 (Fig. 1), are represented by the Puesto Viejo Group (Stipanicic et al., 2007). It consists of 68 ca. 1000 m thick alluvial to fluvial sedimentary sequences intercalated with 69 volcanoclastic rocks, tuffs, basalts, andesite intrusives and rhyolitic ignimbrites 70 accumulated from the early Middle to early Late Triassic interval. The Puesto Viejo 71 Group includes the lower Quebrada de los Fósiles Formation and the upper Río Seco de 72 la Quebrada Formation (Stipanicic et al., 2007). The contact between the basal unit and 73 the volcanic basement of Middle Permian–Lower Triassic Choiyoi Group is an erosional 74 unconformity (González Díaz, 1972). The upper unit is overlain unconformably by the 75 Miocene Aisol Formation (González Díaz, 1972). The complete stratigraphy and origin 76 of the units of the San Rafael Basin have been summarized by Domeier et al. (2011), 77 Ottone et al. (2014) and Monti & Franzese (2016, 2019). The basal part of the Quebrada 78 de los Fósiles Formation consists of coarse epiclastic strata related to proximal alluvial 79 fan systems, sometimes covered by pyroclastic flows. Finer grained levels of the upper 80 section of the Quebrada de los Fósiles Formation represent meandering fluvial systems of 81 low to high sinuosity that were also interrupted by the emplacement of pyroclastic flows 82 (Spalletti, 1994; Monti & Franzese, 2016, 2019). The upper unit, the Río Seco de la 83 Quebrada Formation, is constituted by deposits of braided to meandering low-sinuosity 84 fluvial systems, and towards the top, by coarse-grained strata interpreted to represent the 85 distal sections of alluvial fans intercalated by lava flows (Monti & Franzese, 2016, 2019). 4 86 At its type section, the Quebrada de los Fósiles Formation initiates and culminates 87 with pyroclastic flow (ignimbrite) deposits. The uppermost rhyolitic ignimbrite level 88 marks the boundary with the overlying Río Seco de la Quebrada Formation. Ottone et al. 89 (2014) performed SHRIMP U–Pb radiometric dating from juvenile magmatic zircons of 90 the upper ignimbrite deposit which provided an age constraint of 235.8±2 Ma. Domeier et 91 al. (2011) carried out 40Ar/39Ar isotopic dating on volcanoclastic and ignimbritic rocks 92 from the basal levels of the Quebrada de los Fósiles Formation which yielded an age of 93 ~245 Ma. Recently, the basal ignimbrite has been dated using LA-ICPMS U–Pb 94 indicating a late Anisian age (Monti in Sato et al., 2015). Thus, the Quebrada de los 95 Fósiles Formation as a whole, was deposited from the Middle (late Anisian) to early Late 96 (Carnian) Triassic, being mostly constrained to the Ladinian (Cohen et al., 2018) (Fig. 2). 97 Monti (2015) and Monti & Franzese (2016, 2019) gave full details of the litho- 98 sedimentological description of both units integrating the Puesto Viejo Group and defined 99 five depositional systems: 1) debris-flow deposits, 2) channel-fill deposits, 3) floodplain 100 deposits, 4) pyroclastic deposits, and 5) volcanic intrusives and effusives. For detailed 101 lithofacies analysis of the Quebrada de los Fósiles Formation, we refer to these 102 mentioned contributions. 103 The Quebrada de los Fósiles flora recorded at the type locality of the unit was initially 104 referred as “Pleuromeia flora” composed only of scarce remains of lycophytes and 105 sphenophytes (Morel & Artabe, 1994; Coturel et al., 2016). Recently, Cariglino et al. 106 (2018) described a new, more diverse macrofloral assemblage of Ptilozamites, 107 Pleuromeia, Lepacyclotes, Equisetites and Neocalamites from the Quebrada de los 108 Fósiles Formation at its type locality. This unique and exceptional novel plant assemblage 5 109 of the lower unit of the Puesto Viejo Group includes typical Northern Hemisphere 110 Ptilozamites and Lepacyclotes genera—recorded for the first time in Gondwana— 111 together with Pleuromeia as a typical Middle Triassic assemblage recorded in the 112 Quebrada de los Fósiles Formation (Cariglino et al., 2018). 113 Ottone & García (1991) systematically described for the first time the palynoflora 114 from the type locality of Quebrada de los Fósiles Formation. Vázquez (2013) described a 115 microflora assemblage from the Quebrada de los Fósiles Formation at the Río Seco de la 116 Quebrada creek (see more details in Ottone et al., 2014: 193). During several field 117 seasons from 2010 to 2018, new palynological assemblages were recovered from the 118 Quebrada de los Fósiles Formation at both creeks which are being studied. Zavattieri et 119 al. (in press) have recently described and illustrated diverse freshwater green algal 120 microfossils and dispersed fungal spores among rich terrestrial palynofloras recovered in 121 the recent years from the upper part of the Quebrada de los Fósiles Formation, Puesto 122 Viejo Group. 123 The microfloras were recovered from three sectors of the type section of the Quebrada 124 de los Fósiles Formation, cropping out at the homonymous