Mariana Brea

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.

A new approach to Corystospermales based on Triassic permineralized stems from Argentina

Anatomically preserved mature stems of late Middle Triassic corystosperms from the Paramillo Formation of Argentina are described and assigned to Cuneumxylon spallettii gen. nov. et sp. nov. The silicified specimens show features of the pith, primary xylem and successive rings of secondary xylem and phloem. The most striking characteristic is the anomalous secondary growth, represented by secondary xylem bounded by arcs of secondary phloem probably derived from successive repositioned cambia. Cuneumxylon has two kinds of unusual centrifugal secondary growth. The first shows unequal activity of different portions of the cambium on the circumference of the axes; the consequent restriction of cambial activity to certain restricted areas develops wedged stems, which often split. The second produces polyxylic stems following supernumerary cambial activity. As in extant plants growing in arid regions, the included phloem and the associated parenchyma may have had functional value avoiding desiccation of the outer tissues of the stem during droughts. Anatomical features of other Corystospermaceae were used to determine systematic affinities and to establish relationships among medullosans, corystosperms and cycads.

Rhexoxylon brunoi Artabe, Brea et Zamuner, sp. nov., a new Triassic corystosperm from the Paramillo de Uspallata, Mendoza, Argentina

Abstract A new species of Rhexoxylon from the Upper Triassic of Argentina is described. The material was collected at El Paramillo de Uspallata area and comes from Los Colorados Formation. There is a big buried specimen and scattered material which is preserved by silicification, corresponding to an adult eccentric, oval trunk, whose diameter is 71×58 cm. Three zones can be distinguished: pith, vascular (with perimedullar bundles and centrifugal wedges of secondary xylem) and cork layer. Rhexoxylon brunoi Artabe, Brea et Zamuner, sp. nov . has a heterogeneous pith with parenchyma cells and idioblasts. Perimedullar bundles make up two cycles; the first one is complete constituted by double collateral bundles, facing each other, with secondary growth. The second one is incomplete, showing just the centripetal xylem sector. Peripheral centrifugal secondary xylem wedges show extensive development, reaching up to 38 cm of thickness. The tracheids of secondary xylem have opposite uni- to biseriate bordered radial pitting, and crossfields with one or two simple, slanted lenticular pits. Outside of the xylem a cork layer of about 2 cm persists conforming a longitudinally and transversely fractured rhytidome-like zone. Rhexoxylon brunoi shows a morpho-structural pattern determined by high activity of normal cambium, moderate activity of supernumerary cambium and scarce activity of remanent cambium.

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.

Ecological reconstruction of a mixed Middle Triassic forest from Argentina

Brea, M., Artabe, A. & Spalletti, L.A., December, 2008. Ecological reconstruction of a mixed Middle Triassic forest from Argentina. Alcheringa 32, 365–393. ISSN 0311-5518. The palaeoecology of an in situ Middle Triassic forest known as the Darwin Forest, from the Paramillo Formation of Argentina, is described based on palaeobotanical, sedimentological and spatial analyses. The palaeoforest grew on an andisol soil that developed on volcaniclastic floodplain deposits. The volcanic detritus and the rhythmic amalgamation of upper flow-regime tractional deposits overlying the andisol indicate that the forest was buried rapidly by a subaerial, cool and wet pyroclastic base surge flow. The plant community was reconstructed by quantitative mapping of the fossilized stumps integrated with taxonomic and sedimentological information. The Darwin Forest had a tree density of 427–759 per ha, with an upper stratum (20–26 m) of corystosperms and a second stratum (16–20 m) of conifers. Estimated biomass is equivalent to modern dry monsoonal forest. The understorey was composed of ferns (Cladophlebis spp.). Quantitative growth-ring analysis of Araucarioxylon protoaraucana suggests that these trees were evergreen and, together with vegetation structure and sedimentary data, indicate that the forest developed under dry, subtropical, strongly seasonal conditions.

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.

An anatomically preserved stem from the Carboniferous of Gondwana: Phyllocladopitys petriellae Brea and Césari, sp. nov.

Phyllocladopitys petriellae Brea and Cesari, sp. nov. occurs in the early Late Carboniferous Jejenes Formation, Argentina. The description of the taxon is based on one anatomically preserved stem, a few centimeters in diameter. The primary xylem is mesarch. The secondary xylem shows only inconspicuous growth rings. Pitting on the walls of the tracheids is bordered. Rays are low, uni- or biseriate. Two to four simple pits are present in the cross fields. Comparisons are made with early gymnosperms and Cordaitales and palecolimatic evidence is analyzed.

Leños Fósiles De Leguminosas de la Formación Ituzaingó, Entre Ríos, Argentina: Implicancias Paleoecológicas y Paleobiogeográficas

Abstract. FOSSIL WOODS OF LEGUMINOSAE FROM THE ITUZAINGÓ FORMATION, ENTRE RÍOS, ARGENTINA: PALEOECOLOGICAL AND PALEOBIOGEOGRAPHIC IMPLICATIONS. The family Fabaceae is among the best represented in the fossil record of the Cenozoic of Argentina and in particular of the Ituzaingó Formation. This paper describes four types of permineralized by silicification woods related to this family, Menendoxylon vasallensis Lutz, Anadenantheroxylon villaurquicense Brea, Aceñolaza y Zucol emend., Prosopisinoxylon americanum sp. nov. and Gleditsioxylon paramorphoides sp. nov. Two new fossil species were recognized and the diagnosis of Anadenantheroxylon villaurquicense was amended. The specimens were found in the Ituzaingó Formation (Pliocene—Pleistocene), Entre Rios, Argentina, and have only preserved the anatomy of secondary xylem. Some anatomical features were related with the presence of a seasonal and dry climate. From paleogeographic and paleoecological features of distribution of most related extant genera, it is proposed that during the Pliocene—Pleistocene developed a heterogeneous environment characterized by having arboreal elements linked to Chaco, riparian and component of Seasonally Dry Tropical Forests (SDTF). The presence of the studied fossil wood in the Ituzaingó Formation (Pliocene—Pleistocene) in the Paraná Basin shows a rich flora linked to SDTF southermost of its current distribution, supporting the hypothesis that had a greater extent in South American continent during the late Cenozoic.

El registro de maderas fósiles de Leguminosae de Sudamérica

The fossil wood record of Leguminosae from South America. the Leguminosae has an extensive fossil wood record worldwide. In South America 56 records with affinity to Leguminosae were counted. Each record is analyzed and unpublished data is also included. the Leguminosae is the most palaeoxylological diverse family of South America. It has an extensive temporal record, from the Palaeocene to the Pleistocene, and a broad geographical span, from Patagonia to north colombia.

Leños Fósiles de la Formación el Palmar (Pleistoceno Tardío) en el Parque Nacional el Palmar, Entre Ríos, Argentina

Abstract. FOSSIL WOOD FROM EL PALMAR FORMATION (LATE PLEISTOCENE) IN THE EL PALMAR NATIONAL PARK, ENTRE RÍOS, ARGENTINA. This paper analyzes new fossil wood from El Palmar Formation (late Pleistocene) recovered from the El Palmar National Park, central-eastern Entre Ríos province, Argentina. Two new morphospecies of Beilschmiedioxylon Dupéron-Laudoueneix and Dupéron 2005 (Lauraceae) and other of Terminalioxylon Schönfeld 1947 (Combretaceae) are described, as well as Piptadenioxylon chimeloi Suguio and Mussa 1978 (Fabaceae-Mimosoideae) is cited for the first time in Pleistocene deposits of Argentina. This species was described from the ancient alluvial Tietê River “Porto de areia of Itaquaquecetuba”, São Paulo, Brazil. Wood anatomical characters suggest an affinity with the taxa Beilschmiedia taubertiana (Schw. and Mez) Kosterm., Terminalia australis Cambess, and Parapiptadenia Brenan respectively. The relationships and comparisons with the nearest living relatives were used to infer paleogeographic, paleoclimatic and paleoecological requirements. This fossil record suggests warm and humid climatic conditions for central-eastern of Entre Ríos, and during the period comprising the development of this geological formation. The fossil wood would correspond to components of riparian mixed forests (Lauraceae and Combretaceae) and semi-arid mixed forests (Fabaceae).