RESUMENSe describen los microrrestos silicios de origen vegetal (fitolitos), obtenidos de raspados realizados sobre residuos alimenticios en las paredes internas de recipientes cerámicos utilitarios datados en 730 ± 80 AP y 920 ± 60 AP, procedentes de la Localidad Arqueológica Meliquina, ubicada a 40° 19´ S y 71° 19´ O (Departamento Lácar y Parque Nacional Lanín, Provincia de Neuquén, Patagonia Argentina). Se destaca la presencia de fitolitos del tipo Wavy top y Ruffle top rondel correspondientes a Zea mays (maíz), constituyendo el registro preincaico más austral del continente, cuyo origen es concordante con momentos de disminución de la humedad ambiental en general que habrían incidido en movilidad social y circulación de bienes a larga distancia, con una acentuada territorialidad oriental cordillerana de las sociedades complejas de los valles centrales del centro-sur de Chile entre 1.000 a 700 años AP.PALAbRAS CLAVE: fitolitos, maíz, economías mixtas, Patagonia. IDENTIFyING MAIZE RESIDUES IN POTTERy VESSELS INNORTHWESTERN PATAGONIA, ARGENTINA AbSTRACT Plant opal silica bodies (phytoliths) obtained from scraped food residues from the inside walls of pottery vessels are described and identified as maize (Zea mays, Poaceae) cob bodies. These vessels come from the archaeological locality of Meliquina (-40° 19´S -71° 19´W), Lácar Department and Lanín National Park, Patagonia, Argentina and were dated between 730 ± 80 bP and 920 ± 60 bP. The presence of short-cell phytoliths diagnostic of maize cobs, called wavy-top rondels and ruffle-top rondels from the Zea mays (maize) is highlighted. It constitutes the southernmost preincaic record in the continent, whose origin is related to environmental conditions of low humidity, which would have affected social mobility and the trade of goods through long distances from east to west, with the societies of the central valleys of mid-southern Chile settled to the east of the Andean range between 1,000 and 700 years bP.
Tlie spores of the following genera of Polypodiaceae growing in northwest Argentina were analyzed: Campyloneurum, Microgramma, Pecluma, Phlebodium, Pleopeltis and Polypodium. The study involved analyses of herbarium material using light microscopy and scanning electron microscopy. The spores are monolete, 40-90 [im in major equatorial diameter, eliptic to oblong in polar view and plane to concave-convex in equatorial view. The exospore ranges from 2-5 |im thick, is apparently double-layered, with a verrucate or tuberculate surface that is usually perforated. The perispore ranges from 0.3-1 [am thick, is apparently single-layered, attached to the exospore, perforated, and generally smooth or in some cases micro-ornamented. Most of the taxa analyzed have globules on the surface. These are single or associated in masses and irregularly distributed. Characteristics such as size, shape and exospore and perispore sculpture allow us to differentiate among some of the genera as well as recognize species groups. Microgramma, Campyloneurum, Pecluma, Pleopeltis and Polypodium have verrucate spores whereas those of Phlebodium are tuberculate.
Two Pleistocene sedimentary units are recognized in the Corrientes province, Argentina: the Toropí and Yupoí formations. These sediments have proven productive for fossil vertebrates, but few macrofossils have been recovered. To remedy this situation, plant silica (phytoliths) were extracted from the sediments, enabling a direct comparison of paleovegetation data and information based on previous study of vertebrates. The studied samples (n=28) come from two profiles from the Toropí Stream (28°36´S; 59°02´W), near Bella Vista, Corrientes, from which two Quaternary mammals, Lestodon (Xenarthra) and Hippocamelus (Artiodactyla), have previously been excavated. All samples were productive and contained both non-plant biogenic silica (diatoms, sponge spicular, chrysophyte cysts) and phytoliths. Phytolith assemblages were dominated by morphotypes diagnostic of grasses, in particular C 3 pooids, C 4 chloridoids, and C 3 or C 4 panicoids (or related grasses in the PACMAD clade). Rare phytoliths of palms and other woody or herbaceous dicotyledonous angiosperms were also present. This combination of C 3 and C 4 grasses, and rare palms and other forest indicators, indicates grass-dominated habitats with groves with palms and other trees/shrubs along rivers, growing under a relatively warm and dry climate. This mixed plant community reflects shifting biogeographic affinity with the Chacho-Pampean plain and inter-tropical regions, respectively, linked to the frequent climaticenvironmental fluctuations during the Late Pleistocene.
The Triassic Cuyo rift Basin is one of the renowned petroleum systems in South America that records distinctive alluvial, lacustrine and fluvial settings with volcanic input. The present study focuses on the clay mineral assemblages that represent the syn‐rift to post‐rift fills. Four clay mineral assemblages are defined based on X‐ray diffraction, optical and electron microscopy analyses. The illite/mica‐dominated assemblage is documented in the syn‐rift I (Cerro de las Cabras Formation). Such mineral phases are inherited and derived from the erosion of pre‐rift units, suggesting that physical weathering associated with a warm and semi‐arid climate played a leading role in their occurrence. Authigenic smectite clays are diagnostic in organic‐lean mudstones of the syn‐rift II (lower Potrerillos Formation) which point to alteration of pyroclastic material under a warm and semi‐arid to humid climate. A warm and humid climate prevailed during the deposition of lacustrine hydrocarbon source rocks (upper Potrerillos and Cacheuta formations). Organic‐rich mudstones show the illite/mica–kaolinite–smectite assemblage in conjunction with amorphous organic matter and restricted terrigenous elements. Diagenetic kaolinite booklets and bipyramidal quartz are attributed to the acidification of pore‐water related to kerogen transformation during burial diagenesis. Vitrinite reflectance values (ca 0.63%) confirm that organic‐rich sediments reached the earliest oil window; however, smectite is devoid of illite layers throughout the Triassic succession, probably related to the absence of potassium in the system and the high crystallinity of the smectite, which delayed the transformation of smectite into mixed layers illite–smectite. Red mudstones of the post‐rift II (the fluvial‐lacustrine Rio Blanco Formation) show the kaolinite‐dominated assemblage where the authigenic kaolinite is interpreted to be derived from the alteration of volcaniclastic detritus and indicative of warm climate with markedly wet periods.
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