Eduardo M. Morel

Devonian plants from Colombia, with discussion of their geological and palaeogeographical context

Plant fossils are described from the Cuche Formation, Eastern Cordillera, Colombia in the area of Floresta. Those identified as Colpodexylon cf. deatsii Banks and cf. Archaeopteris sp. suggest an earliest Late Devonian (Frasnian) age for the formation. These or similar taxa are also found in contemporaneous deposits in western Venezuela, and other elements of the Venezuelan flora are found in a geographically intermediate locality. All three Devonian plant localities in the northwest of South America are within the Colombian Eastern Cordillera and its northern extension, the Venezuelan Perija Range, an area that has been integrated as a part of the so-called ‘Eastern Andean Terrane’ or ‘Central Andean Province’, supposedly accreted to the autochthonous block of the Guyana Shield during the early Jurassic or before. Although both invertebrates and plants from this terrane have strong affinities to North American and European assemblages, and might be interpreted as implying a Laurussian origin for the Eastern Andean Terrane, the evidence is not yet unequivocal, with some authors postulating an in situ development of this province.

Geological Factors and Evolution of Southwestern Gondwana Triassic Plants

Abstract A synergistic model based on reciprocal influences between biotic and abiotic factors is developed for the Triassic of southwestern Gondwana. Changes in physical environment exerted a strong influence on the characteristics and evolution of plant assemblages. The Permian-Triassic extinction, and the change from palaeophytic to mesophytic floras, is one of the most striking examples of direct influence of physical environment upon plant communities. Pangea coalescence, the distribution of land masses and seas, the spreading of continental climates (megamonsoonal conditions) and the waning polar glaciation determined the expansion of xeromorphic morphotypes that became dominant during the whole Mesozoic. In southwestern Gondwana, the introduction or invasion of immigrant lineages suggests a strong asymmetrical interchange from the Euroamerican realm to the Gondwana realm. In addition, generalised extensional volcanism, development of intracratonic rifts and the palaeolatitudinal location of climatic zones during the early-Middle Triassic favoured extinction of the Glossopteris flora and explosive diversification of endemic groups. From the chronological viewpoint, the Barrealian, Cortaderitian and Florian stages are recognised in the Triassic of southwestern Gondwana. These stages are respectively characterised by: (a) appearance of mesophytic elements, and coexistence of Palaeozoic and Mesozoic groups, (b) maximum diversification of the Dicroidium flora, and (c) Dicroidium flora decline and replacement by morphotypes with strong Jurassic affinity. These palaeofloristic changes seem to be strongly influenced by tectonic evolution of sedimentary basins, temporal and regional distribution of sedimentary environments, and intra-Triassic palaeoclimatic change.

Triassic floras of Argentina: Biostratigraphy, floristic events and comparison with other areas of Gondwana and Laurasia

Study of the Triassic floristic record of several stratigraphic units of southern and west‐central Argentina has permitted recognition of five Assemblage Biozones and three Stages, defined on the basis of Assemblage Biozone chronology, analysis of main stratigraphic unconformities, and evolution of basin infill. These stages are each characterised by a floristic events: a) appearance of mesophytic elements and coexistence of Palaeozoic and Mesozoic groups (Barrealian); b) maximum diversification of the Dicroidium Flora (Cortaderitian); and c) decline of the Dicroidium Flora and replacement by morphotypes with strong Jurassic affinity (Florian). The Triassic geological record of Argentina, notable for the remarkable continuity of fossil floras, has great potential for long‐distance correlations. Using floristic events recognised in SW Gondwana, a global chart shows the bio‐ and chronostratigraphic units, and compares them with Triassic floras described from the Eastern Province of extratropical Gondwana, and Laurasia.

Middle Devonian lycopsids from high southern palaeolatitudes of Gondwana (Argentina)

Fossil plants are described from the upper part of the Devonian Lolen Formation, Sierra de la Ventana, Buenos Aires Province, Argentina, in the area of Estancia Las Acacias. The sequence is composed mainly of dark grey shales, and fossils were found in a single horizon where thin inter- layered beds of fine reddish-brown micaceous sandstones appear where the environment of marine deposition became more shallow. The age of the Lolen Formation is presently established on the basis of brachiopods, these being characteristic elements of the Malvinokaffric realm from the Gondwana Lower Devonian (Emsian). The fossil plants are remarkably preserved given that they are in rocks that have undergone intense deformation. The plants are identified as Haplostigma sp. and Haskinsia cf. H. colophylla, and suggest a Middle Devonian age (Givetian) for the fossil-bearing levels. Haskinsia, identified on the basis of leaf morphology, is the first well-delimited Middle Devonian lycopsid genus described from Argentina, and the record from the most southerly palaeolatitude. During the Middle Devonian, Haskinsia was distributed in tropical, warm temperate and high southern latitude, ?cool temperate zones.

Estratigrafía, facies y paleoflora de la sucesión triásica de Potrerillos, Mendoza, República Argentina

Nuevas exposiciones en localidades triasicas clasicas como las de los cerros Bayo y Cocodrilo (Potrerillos, noroeste de la Provincia de Mendoza, Argentina) permitieron (1) describir y caracterizar las formaciones Rio Mendoza, Cerro de Las Cabras, Potrerillos y Cacheuta; y (2) mejorar el conocimiento bioestratigrafico de las sucesiones triasicas basandose en el hallazgo de nuevos registros de plantas fosiles. Dos secciones verticales fueron estudiadas en detalle, y el analisis de las litofacies ha sido usado para interpretar los sistemas de deposicion. Facies gruesas de abanico aluvial caracterizan a la Formacion Rio Mendoza y a la seccion inferior de la Formacion Potrerillos. Sistemas fluviales traccionales gravosos y arenosos aparecen hacia el techo de la Formacion Rio Mendoza y en distintos intervalos de la Formacion Potrerillos. En el tramo basal de la Formacion Cerro de Las Cabras y en la mayor parte de la Formacion Potrerillos se identificaron depositos de sistemas fluviales de alta sinuosidad y de planicies de inundacion. Finalmente, algunos intervalos de la Formacion Potrerillos y mas especificamente la Formacion Cacheuta estan dominados por sucesiones de lutitas negras generadas por procesos suspensivos en lagos meromicticos. En asociacion con los depositos mencionados, secuencias progradacionales discretas de areniscas y conglomerados sugieren el desarrollo de barras de desembocadura hipopicnales y de canales distributarios. Se individualizaron 16 niveles fosiliferos con 23 taxones: Equisetites fertilis, Neocalamites carrerei, Cladophlebis mesozoica, C. mendozaensis, Dicroidium argenteum, D. dubium, D. odontopteroides, Johnstonia coriacea, J. stelzneriana, Xylopteris elongata, Zuberia feistmanteli, Feruglioa samaroides, Pachydermophyllum praecordillerae, Kurtziana cacheutensis, Sphenobaiera argentinae, Baiera africana, B. cuyana, Yabeiella mareyesiaca, Y. spathulata, Y. brackebuschiana, Fraxinopsis andium y Gontriglossa sp. y Rochipteris sp. Se describieron 16 tafocenosis que se relacionaron con los respectivos ambientes de sedimentacion. El analisis de las tafocenosis y su vinculacion con las facies y paleoambientes de acumulacion permitio reconocer en la localidad tipo de la Formacion Potrerillos a dos biozonas de asociacion en continuidad estratigrafica (Yabeiella mereyesiaca-Scytophyllum bonettiae-Protophyllocladoxylon cortaderitaensis -MBC- y Yabeiella brackebuschiana-Scytophyllum neuburgianum-Rhexoxylon piatnitzkyi -BNP-). La Formacion Potrerillos en este sector de la cuenca se desarrollo durante el Triasico Medio tardio-Triasico Tardio temprano

Primitive Vascular Plants and Microfossils from the Río Seco de los Castaños Formation, San Rafael Block, Mendoza Province, Argentina

In this contribution we describe fossil plant remains from Rio Seco de los Castanos Formation, at San Rafael Block , Mendoza Province, Argentina. The fossil plants comprise non-forked and forked axes without or with delicate lateral expansions, which are assigned to Bowerophylloides cf. mendozaensis and Hostinella sp. We refer them to primitive land plants and discuss about their systematic affiliation. Furthermore, we mention the presence of a diverse acritarch assemblage present in the same lithostratigraphic unit. On the basis of the taxonomical information and stratigraphic correlation, we could infer that Rio Seco de los Castanos Formation has an Early Devonian age. The taphonomical conditions of this fossil association would indicate that the plants were transported some distance from their presumed coastal and riverbank habitats. Finally, studying the amount and the percentage of kaolinite within charcoal levels, warm to cool temperate paleoclimatic conditions were deduced.

Revisión De La Paleoflora De La Formación Nestares (Jurásico Temprano), Provincias Del Neuquén y Río Negro, Argentina

Abstract. REVIEW OF THE PALEOFLORA OF THE NESTARES FORMATION (EARLY JURASSIC), NEUQUÉN AND RÍO NEGRO PROVINCES, ARGENTINA. In this contribution the paleoflora of the Nestares Formation, exposed along both banks of the Limay River, close to the Alicurá dam (northwest of the Northpatagonian Massif) was reviewed. A sedimentological profile was measured, four fossil-bearing levels were identified and the systematic study allowed the identification of 18 taxa, 12 of which were previously described for this site= Neocalamites carrerei (Zeiller) Halle, Marattia muensteri (Goeppert) Zeiller, Goeppertella diazii Arrondo and Petriella, Kurtziana brandmayri Frenguelli, K. cacheutensis (Kurtz) Frenguelli, Taeniopteris sp., Otozamites albosaxatilis Herbst, O. ameghinoi Kurtz, O. bechei Brongniart, O. hislopii (Oldham) Feistmantel, Ptilophyllum acutifolium Morris in Grant, Elatocladus confertus (Oldham and Morris) Halle and six that are new for this formation= Equisetites frenguellii Orlando, Archangelskya protoloxsoma (Kurtz) Herbst, Sagenopteris nilssoniana (Brongniart) Ward, Nilssonia taeniopteroides Halle, O. bengalensis Oldham and Morris, and Elatocladus planus (Feistmantel) Seward. These records are added to 6 other previously studied taxa, including Cladophlebis mendozaensis (Geinitz) Frenguelli, C. oblonga Halle, Gleichenites cf. sanmartini Halle emend. Herbst, Scleropteris vincei Herbst, Araucarites phillipsi Carruthers, Podozamites elongatus (Oldham and Morris) Halle, providing an updated list of 24 taxa for this unit. The compositional similarity with other Early Jurassic paleofloras from Argentina indicates a Sinemurian age.