Alejandro F. Zucol

Phytolith analysis of Cyperaceae from the Pampean region, Argentina.

Cyperaceae, along with Poaceae, is the main silica accumulator. Although the anatomical-taxonomic and palaeobotanical relevance of phytoliths has been well established, there are no studies that deal with the qualitative and quantitative aspects of the phytolith production or differentiate phytoliths from the different organs in Cyperaceae. Toward the construction of a detailed database of phytolith production, we describe in the present paper the phytoliths of leaves, culms and fruits of Cyperaceae from Pampean region (Argentina). Phytoliths were extracted by a calcination technique. Qualitative and quantitative characters and percentages of phytolith morphotypes were subject to principal component analysis to analyse their taxonomic relevance. For some sedges, values of phytolith content and a comparative analysis of leaves, culms and fruit phytoliths are presented here for the first time. Diverse tissues such as epidermis, xylem, parenchyma and sclerenchyma produced phytoliths. The most abundant morphotypes were conical phytoliths, which showed differences in the base shape and in their size between organs. Leaf/culm cones have a rounded, rectangular or square base; typical fruit cones have a polygonal base and they are bigger and more robust. PCA showed that quantitative and qualitative characters of cones, along with the percentages of morphotypes, allowed group distinction.

Early Paleogene climate at mid latitude in South America: Mineralogical and paleobotanical proxies from continental sequences in Golfo San Jorge basin (Patagonia, Argentina)

The Paleocene-Eocene boundary was a period of transient and intense global warming that had a deep effect on middle and high latitude plant groups. Nevertheless, only scarce early Paleogene paleoclimatic records are known from the South American continental sequences deposited at these latitudes. In this contribution clay mineralogy and paleobotanical analyses (fossil woods and phytoliths) were used as paleoclimate proxies from the lower and middle parts of the Rio Chico Group (Golfo San Jorge basin, Patagonia, Argentina). These new data may enable to understand the changing climatic conditions during part of the Paleocene-Eocene transition. In this setting, three clay mineral assemblages were identified: S1 assemblage (smectite) dominates the Penas Coloradas Formation; S2 assemblage (smectitegt;kaolinite) occurs in the stratigraphic transition to the Las Flores Formation; and S3 assemblage (kaolinitegt;smectite) dominates the Las Flores Formation. These trend of change in the detrital clay mineral composition is interpreted as resulting mainly from the changing paleoclimatic conditions that shifted from seasonal warm temperate to tropical affecting the same source area lithology. Moreover, the paleobotanical data suggest that the Early Paleogene vegetation in the Golfo San Jorge basin underwent significant composition and diversity changes, ranging from mixed temperate - subtropical forest to mixed subtropical - tropical, humid forest. The integrated analysis of the clay mineral composition and the palaeobotanical assemblages suggests that, in central Argentinean Patagonia, the Paleocene-Eocene climate changed from temperate warm, humid and highly seasonal precipitation conditions to subtropical-tropical, more continuous year-round rainfall conditions.

Fossil wood of the Mimosoideae from the early Paleocene of Patagonia, Argentina

Brea, M., Zamuner, A.B., Matheos, S.D., Iglesias, A. & Zucol, A.F., December, 2008. Fossil wood of the Mimosoideae from the early Paleocene of Patagonia, Argentina. Alcheringa 32, 427–441. ISSN 0311-5518. An anatomically preserved mature stem from the Salamanca Formation (early Paleocene) at Palacio de Los Loros, central Patagonia, Argentina, is described and assigned to Paracacioxylon frenguellii sp. nov. The material was preserved by siliceous permineralization and shows features of the secondary xylem typical of subfamily Mimosoideae. This species represents the oldest record of the genus and of the Leguminosae along the western border of Gondwana, and is the worlds second oldest record of Leguminosae wood. The species is characterized by ring-porous to semi-ring-porous vessels that are solitary, in multiples of 2–4 and clustered, simple perforation plates, alternate and vestured inter-vessel pitting, homocellular 1–6 seriate rays, tyloses, crystals and diffuse apotracheal, vasicentric paratracheal and confluent axial parenchyma. Paracacioxylon frenguellii has anatomical similarities to Acacia Miller. The presence of Paracacioxylon frenguellii associated with pulvinate leaves suggests that the legumes might have been a component of mesothermal forests developed along the western margin of the Golfo San Jorge Basin during the early Paleocene.

Paleoecology and paleoenvironments of Podocarp trees in the Ameghino Petrified forest (Golfo San Jorge Basin, Patagonia, Argentina): Constraints for Early Paleogene paleoclimate

During the Early Paleocene (Danian), Central Patagonia had a warm-temperate climate and was dominated by evergreen coniferous forests. Abundant permineralized conifer woods along with some dicot and palm leaf compressions were found in the Ameghino Petrified Forest, and provide evidence of this type of flora. All the permineralized wood and large trunks recovered were assigned to the species Podocarpoxylon mazzonii. An estimated tree height of 17-29m was calculated on the basis of diameter measurements. Based on 14 ring sequences, with a total of 169 rings, the mean ring width and Mean Sensitivity (MS) were 1.23 and 0.19mm respectively. The growth rings are moderately wide, extremely uniform and complacent, indicating that the environment was favourable and constant, and lacked significant stress factors limiting tree growth. Following the quantitative analysis for conifers outlined by Falcon-Lang, the growth ring anatomy of the Podocarpoxylon mazzonii suggests that these trees had an evergreen habit. The combination of the fossil flora, growth ring, and sedimentological analyses suggest that this mostly evergreen coniferous forest developed under warm-temperate conditions and without limiting factors.

ANÁLISIS FITOLÍTICO DE LA FORMACIÓN TEZANOS PINTO (PLEISTOCENO TARDÍO–HOLOCENO TEMPRANO) EN EL SECTOR SUDOESTE DE LA PROVINCIA DE ENTRE RÍOS (ARGENTINA)

Abstract. PHYTOLITH ANALYSIS OF TEZANOS PINTO FORMATION (LATE PLEISTOCENE-HOLOCENE) IN THE SOUTHWESTERN REGION OF ENTRE RÍOS PROVINCE (ARGENTINA). Loess deposits are the main component of the Late Quaternary sequences of the Pampa plains (South America). The Last Glacial Maximum loess represents a depositional unit of the Pampean Aeolian System that evidences the expansion of semiarid conditions to the northeast of the region. The Tezanos Pinto Formation is the typical loessic unit of the late Pleistocene—early Holocene of the northeastern Pampa region. Advances in the knowledge of the micropaleobotanical content of this geologic formation are presented in this work, especially the obtained results of the Southweastern area of Entre Ríos Province. The analyzed phytolith assemblages show a high homogeneity with some variations that allowed their quantitative differentiation across the analyzed sedimentary profiles. The presence of grass phytoliths jointly with palm, podostemoid and ciperoid elements allowed to make this characterization. The described phytolith assemblages, as previously observed in the northwestern part of the area covered by the loess in Entre Ríos, show high abundance of megathermic grasses, with a greater presence of xeric elements at lower levels, and with elements denoting warm-temperate episodes with major moisture principally in their middle and top sections. This is linked to the presence of a warm-temperate to temperate steppe with xeric conditions in the basal levels.

ANÁLISIS FITOLÍTICOS EN SUELOS FORMADOS SOBRE ANTIGUAS TERRAZAS DEL RÍO URUGUAY (COLÓN, ENTRE RÍOS): PRIMERA EVIDENCIA DE RETRACCIÓN DE LOS PALMARES DE BUTIA YATAY (MART.). BECC.

Resumen . Los palmares de Butia yatay (Mart.) Becc. en el Parque Nacional El Palmar (Colon, Entre Rios), son comunidades relictuales que se desarrollan sobre los suelos arenosos que pertenecen al orden de los Entisoles. Estos suelos constituyen las terrazas antiguas del rio Uruguay. La serie de suelos Puerto Yerua son suelos arenosos pardos formados sobre terrazas y poseen un mayor desarrollo pedologico. Se ha estudiado la composicion fitolitica de la secuencia pedologica de esta serie de suelos con la finalidad de contribuir al conocimiento de la flora que acompano el desarrollo de los mismos. Las asociaciones fitoliticas observadas reflejan el cambio de dos ciclos pedologicos, que dividen al perfil analizado en dos zonas demarcadas por la presencia de diferentes paleocomunidades: una de palmares asociados a un estrato herbaceo pobre y una superior de pastizales meso-megatermicos con escasa presencia de microrestos afines a elementos arboreos. El registro fitolitico descripto en el presente trabajo es el primer antecedente que muestra el posible punto de cambio en la fisonomia del paisaje y la retraccion de los palmares de yatay en el area de estudio. PALABRAS CLAVE. Silicofitolitos, Serie Puerto Yerua, Parque Nacional El Palmar, Rio Uruguay, Paleoambientes. Abstract. PHYTOLITH ANALYSIS OF SOILS FORMED OVER OLD TERRACES OF THE URUGUAY RIVER (COLON, ENTRE RIOS). FIRST EVIDENCE OF RETRACTION OF BUTIA YATAY (MART.) BECC. PALM FOREST. The Butia yatay (Mart.) Becc. palm forest in the El Palmar National Park (Colon, Entre Rios) is part of a relict community developed over sandy soil, belonging to the Entisols order of the old terraces of the Uruguay River. The Puerto Yerua soil series are gray sandy soils formed on terraces that have greater pedological development. The phytolith assemblages of this pedological sequence have been studied in order to contribute to the knowledge of the flora that accompanied the development of these series. The phytolith associations observed has reflected the change of two pedological cycles in which the analyzed profile is divided, with two zones demarcated by the presence of different paleocommunities: one is a palm forest associated with a poor herbaceous stratum, and an upper stratum of meso-megathermic grassland with scarce presence of remains with affinity to arboreal elements. The phytolith record described in this paper is the first record that shows the possible location of the change in the physiognomy of the landscape and the retraction of the Butia yatay palms in the study area. KEY WORDS. Silicophytoliths, Puerto Yerua soil series, El Palmar National Park, Uruguay River, Paleoenvironments.

Registros biosilíceos en sitios arqueológicos de las sierras de Tandilia Oriental, Argentina (Pleistoceno Tardío-Holoceno Tardío): Consideraciones paleoambientales

Biosiliceous records in the western Tandilia range archaeological sites, argentina (Late PleistoceneLate Holocene): Paleoenvironmental considerations.The biosiliceous records from two archaeological sites Abrigo Los Pinos (LPn) and Abrigo La Grieta (LG) located in the eastern Tandilia range (Pampean region, Argentina) are analyzed. �uman occupations in these sites contain a high diversity of archaeological remains (lithic, ceramic, bones, mineral pigments, charcoal and rock art). The long sequences, which span from the late Pleistocene to the late �olocene allow us to study the palaeonvironmental setting of early occupations. Phytolith assemblages from the middle sections in both profiles are dominated by panicoid elements, indicating temperate (LG) and warm conditions (LPn), coinciding with moments of greatest human occupation sites (�olocene in LG and early to middle �olocene in LPn). �owever, at basal and top levels of the sequences, environments are dominated by drier and cooler episodes which are mainly alternated by wet conditions in LG. The present analysis brings information about the plant component along the sequences and estimates that microenvironmental conditions inside the caves were fluctuating and comparable between anthropic levels.