Palynoflora from the La Anita Formation (Maastrichtian), Austral-Magallanes Basin, Argentina

Here we describe the spore and pollen assemblages recovered from the La Anita Formation, Late Cretaceous, Austral-Magallanes Basin (~50°S). This unit shows a high diversity of spores, with subordinate gymnosperms (mainly represented by Podocarpaceae) and angiosperms (mainly represented by Proteaceae and Arecaceae). The abundance of these groups varies between the two fertile studied levels, being one dominated by ferns (mainly Cyathidites minor and Laevigatosporites ovatus) and the other by gymnosperms (Podocarpidites spp.). The presence of aquatic ferns (Azollopsis), diverse Podocarpaceae and key angiosperm taxa (such as Arecipites, Clavatipollenites, Dichastopollenites, and Spinizonocolpites) is indicative of warm and hyper-humid conditions. The great abundance of Arecaceae and the presence of some key taxa (e.g. Azollopsis sp., Ericipites scabratus, Peninsulapollis gillii, Proteacidites spp.) support a probable Maastrichtian age for the uppermost strata of the La Anita Formation. The multivariate statistical analysis here conducted showed that the La Anita Formation has its greatest similarity with the La Irene Formation (Maastrichtian from the Austral-Magallanes Basin). Both formations are also related with other coeval palynofloras from Patagonia and Antarctica.


INTRODUCTION
The Late Cretaceous is a critical interval to understand the evolution of floras around the world, a time when angiosperms became dominant components in terrestrial ecosystems for the first time (Friis et al., 2011;Lupia et al., 1999;Nagalingun et al., 2002;Barreda et al., 2019), and a number of new lineages have their origin, such as Proteaceae and Nothofagaceae in the high southern latitudes (e.g. Dettmann & Thomson, 1987, Askin, 1990bCantrill & Poole, 2005). In southern South America terrestrial palynological records are sparse (Papú, 1988a(Papú, , b, 1989Baldoni, 1992;Baldoni & Askin, 1993;Papú, 2002;Povilauskas et al., 2008;Povilauskas, 2010Povilauskas, , 2011Povilauskas, , 2012Povilauskas, , 2013Povilauskas, , 2016Vallati, 2010;Novas et al., 2019), with several geologic units with no information on their spore-pollen content. For this reason, the study of new assemblages is essential for evaluating the evolution of austral floras and will also serve as a basis to better evaluate the magnitude of the drop in plant diversity and abundance throughout the K/Pg boundary (Barreda et al., 2012).
The purpose of this paper is to describe the palynological assemblages recovered from the La Anita Formation (Bianchi, 1967), Austral-Magallanes Basin, Southern Patagonia; to refine the age and the paleoclimatic conditions that prevailed during the deposition of this unit; and, to integrate and compare this results with what is known of Late Cretaceous palynofloras of Patagonia (La Irene, Lefipán, Loncoche, Monte Chico, Cerro Cazador, Allen and Paso del Sapo formations) and Antarctica (Lopez de Bertodano Formation) using statistical methods. This is the first work in a series that aim to study and update the palynological fossil record from the Late Cretaceous in Patagonia in order to better understand the evolution of southern South American floras.

GEOLOGICAL SETTING AND STUDIED SECTION
The La Anita Formation is part of a prograding siliciclastic wedge accumulated during the foreland stage of the Austral-Magallanes Basin (Santa Cruz Province, southern Argentina). It covers the deep-marine Alta Vista Formation, and is covered by continental deposits of the Cerro Fortaleza and La Irene formations (Macellari et al., 1989;Moyano Paz et al., 2018;. The La Anita Formation is character-ized by sandstones and pebbly sandstones, with subordinate mudstones and heterolithic deposits . It was assigned to the Campanian based on both ammonites (Riccardi & Rolleri, 1980, Riccardi, 1983Kraemer & Riccardi, 1997) and detrital zircons (Sickmann et al., 2018;.
The La Anita Formation was interpreted as a delta system with vertical variation on the relative roles of processes affecting it; thus, a wavedominated lower unit and a fluvio-dominated upper unit were defined by Moyano . Both units are separated by a regional erosion surface related to a relative sea level fall. The wave-dominated lower unit grades from the deep-marine fine-grained sediments of the Alta Vista Formation, into a dominantly sandy, graycolored succession. The presence of trace fossils suites and the abundance of wave-generated structures, indicate high-energy conditions, associated with a high recurrence of storm events. However, the low abundance and diversity of these traces could be related to a stressing condition produced by low salinity and bottom oxygenation due to fluvial-discharge effects. The fluvio-dominated upper unit shows a general coarser grain size. It is composed by high-sinuosity, multi-story distributary channels, along with fine-grained deposits related to interdistributary areas, with no evidence of wave nor tidal influence. The upper unit shows evidence of deposition in a brackish-water environment, such as the presence of a trace suite attributable to a stressed expression of the Skolithos ichnofacies.
The studied section crops out 4 km south of Calafate City, Santa Cruz province; at the base of Calafate Hill, in a fresh cliff in the Calafate Creek (50°22'15.67"S 72°14'12.30"W; Fig. 1). This locality represents the uppermost facies of the upper unit of the La Anita Formation, and is characterized by fine-to medium-grained yellowish sandstone bodies with trough-cross stratification, tabular fine dark laminated organic-rich claystones, and channelized sandstone bodies with trough-cross stratification and abundant carbonaceous material (Fig. 2). Fossil leaf compressions of conifers and ferns were found; as well as leaves, fruits and seeds of angiosperms.

MATERIALS AND METHODS
Two levels from the La Anita Formation were productive for palynology: CCC-A from a coal level (collection number MPM-Pb-18963) and CCC-B from a siltstone level (collection number MPM-Pb-18964), both within interdistributary areas on a delta plain fine grained deposits (Fig.  2). Samples were processed following standard palynological techniques, and mounted in a glycerol mounting medium. The observations were made under a Leica DM2500 light microscope and the photographs were taken with a Leica DFC295 digital camera. Specimen locations refer to England Finder coordinates. In order to obtain the relative abundance of plant groups, counts of at least 300 individuals were conducted. Broken individuals were not counted, and tetrads and polyads were counted as one individual. The specimens are stored at the paleobotanical collection of the Museo Regional Provincial "Padre Jesús Molina", Rio Gallegos, Santa Cruz Province (acronym MPM-Pb).

RESULTS
The recovered assemblages from the La Anita Formation at the Cerro Calafate locality are very well preserved and integrated by spores, pollen grains, plant tissue fragments and fungal remains. A total of 42 spores and pollen species were identified, representing 3 bryophytes, 14 ferns, 11 gymnosperms, 13 angiosperms and 1 fresh-water algae ( Table 1).

DISCUSSION AND CONCLUSIONS
The palynoflora recovered from the upper unit of the La Anita Formation suggests two different plant communities. Sample CCC-A has a high relative abundance of Cyathidites minor (both monads and polyads), with Matonisporites equiexinus, Spinizonocolpites hialinus and Zygnemataceae zygospores. The fern family Matoniaceae lives in the tropical regions of southeastern Asia (Tryon & Lugardon, 1990). S. hialinus is related to Arecaceae (Archangelsky, 1973;Martinez et al., 2016) an angiosperm tropical family with low resistance to frosts (Heywood et al., 2007). The Zygnemataceae produce zygospores in clean, oxygen-rich, stagnant, shallow fresh water bodies, where the temperature can rise quickly to the level required for this process (van Geel, 1976). This association suggests a vegetation developed near a lake or a coastal marsh, under hiper-humid and warm conditions. Sample CCC-B represents an inland forest, dominated by Podocarpaceae (Podocarpidites spp.) and Arecaceae (Arecipites minutiscabratus), with a minor presence of Proteaceae (Lewalanipollis sp., Peninsulapollis sp., and Proteacidites sp.).
Most of the spore and pollen species recovered from the La Anita Formation are long-ranging and can only give a general idea about the age of the upper levels of the La Anita Formation. The great abundance of Arecaceae at high and middle latitudes in the southern hemisphere is achieved towards the end of the Cretaceous (Barreda et al., 2012). Also, S. hialinus was recorded in  the Loncoche and Lefipán formations, from the Campanian-Maastrichtian of Patagonia (Baldoni & Askin, 1993;Papu, 2002;Barreda et al., 2012). The oldest palynological record of Proteaceae in the Antarctic Peninsula occurs at the middle Santonian, extending to southern South America at the Campanian-Maastrichtian (Askin & Baldoni, 1998). In Argentina, Peninsulapollis gillii was first recorded from the Los Alamitos Formation of Campanian age (Papú & Sepúlveda, 1995), meanwhile Proteacidites was described in multiple Maastrichtian and Danian sequences (Baldoni & Askin, 1993;Povilauskas, 2010Povilauskas, , 2013Volkheimer et al., 2007). The oldest records of Ericipites scabratus in Patagonia are from the Maastrichtian on both the Lefipán (Baldoni & Askin, 1993) and La Irene (Povilauskas et al., 2008) formations. These records suggest a Late Cretaceous, probably Maastrichtian age for the upper sections of the La Anita Formation. Also, in the studied area, the La Anita Formation is unconformably covered by the Maastrichtian La Irene Formation, restricting its maximum age (Povilauskas et al., 2008).
Based on the cluster analysis, the La Anita Formation shows its greatest similarities with La Irene Formation. These units share 15 species: C. equalis, C. minor, G. senonicus, L. ovatus, T. reticulatus, R. austroclavatidtes, M. antarcticus, P. elegans, P. ellipticus, A. minutiscabratus, E. scabratus, P. gillii, Proteacidites sp., Rhoipites sp., and S. hialinus. The locality of the La Irene Formation studied by Povilauskas et al. (2008) is close both, geographically and stratigraphically, from the one presented here. Both formations share similarities on its inferred floral assemblage (a plant community dominated by ferns and angiosperms, with absence of Nothofagaceae) as well as its depositional conditions (a fluvio-dominated delta environment developed under warm and humid climatic conditions). The two abundance histograms pre- sented by Povilauskas et al. (2008) are also similar with the counts presented here. One level is strongly dominated by trilete psilate spores, with low representation of gymnosperm and angiosperm pollen grains; and the second level shows lesser abundance of spores and an increase in angiosperm pollen grains (mainly Arecaceae and Chloranthaceae). However, the La Anita Formation presents a much greater abundance of Podocarpaceae (67% in CCC-B) than the La Irene Angiosperma incertae sedis. X Spinizonocolpites hialinus Archangelsky & Zamaloa, 1986 Arecaceae X Tricolpites reticulatus Cookson, 1947 Gunneraceae (Gunnera) X Table 1. List of taxa.
The assemblages from the Lopez de Bertodano Formation (Antarctic Peninsula), represent a completely different floral setting: a podocapaceous/Nothofagidites dominated rainforest, with great diversity of Nothofagaceae, Proteaceae and Myrtaceae (Dettmann & Thompson, 1987;Bowman et al., 2014). These palynological assemblages show a mixed of cool temperate palynomorphs (such as Nothofagidites and Phyllocladidites) along with warmer climate indicators (particularly in the late Maastrichtian, such as Peninsulapollis, Bombacacidites and Anacolosidites). The vegetation in the Antarctic Peninsula was probably zoned by altitude, with the megathermic plant associations occupying coastal/lowland areas and cool climate associations in the higher altitude, inland areas (Askin, 1990b). These characteristics separate the palynofloras of the Antarctic Peninsula, from those of Patagonia, resulting in low similarity values among them.
The assemblage from the Allen Formation (Maastrichtian of the Neuquen Basin) have species characteristics from both, southern (Cicatricosisporites, Lewalanipollis, Penninsulapollis, Podocarpidites, and Proteacidites) and paleoequatorial latitudes (Gabonisporis and Tricesticillus). Interestingly, this scenario is somehow comparable to that previously reported for the Early Cretaceous of central Argentina, where a "Transition Zone" was defined (Pramparo, 1990). This unit only shows gross similarities with the La Anita Formation Previous cluster analysis of Campanian-Maastrichtian palynofloras from Patagonia (Povilauskas et al., 2008;Povilauskas, 2016), found great similarities between the Paso del Sapo Formation and other Patagonian palynofloras. However, our analysis shows only gross similarities among them; the observed differences are related to the fact that, in our analysis, we considered all the species recorded in the Paso del Sapo Formation (not only those share with the La Anita Formation) which highlights the high level of endemism of the Paso del Sapo Formation assemblages, with the exclusive presence of Conbaculatisporites sp., Cycadopites follicularis, Cycadopites punctatus, Entylissa sp., Klulcisporites pachydictyus, Laevigatosporiles gracilis, Laevigatosporites vulgaris, Marallisporites scabratus, Momipites fragilis, Podocarpidites verrucosus, and Waltzispora sp. among the most significant.
The new palynological records of the La Anita Formation widen our knowledge of the latest Late Cretaceous floras in southern Patagonia.   Table 2. Counts expressed in absolute frequencies and percentages.
The similarities detected by our cluster analysis helps to refine the composition and geographic distribution of the Late Cretaceous austral vegetation previous to the floral turnover of the Cretaceous-Paleogene boundary.

ACKNOWLEDGMENTS
The authors would like to thank the Secretaría de Cultura de la Provincia de Santa Cruz and the Comisión de Fomento from Tres Lagos Town. To O. Cardenas for processing the palynological materials and L. Villar de Seoane, M. Luengo and S. Richiano for their comments. We are grateful to V. Perez-Loinaze and M. Quattrocchio for their critical comments as reviewers of the manuscript. This research was funded by the Consejo Nacional de Investigaciones Científicas y Técnicas (PIP 1016/10 and PIP 2014-0259) and by the Agencia Nacional de Promoción Científica y Tecnológica (PICT 2012-0828, PICT 2013-0388, and PICT 2017.