Marcelo A. Martínez

Depositional environments and hydrocarbon potential of the Middle Jurassic Los Molles Formation, Neuquén Basin, Argentina: palynofacies and organic geochemical data

A multidisciplinary analysis of palynofacies in a sequence-stratigraphical framework, TOC (total organic carbon) and TAI (thermal alteration index) analyses, has been applied to outcrop samples of the uppermost Los Molles Formation (Middle Jurassic), Neuquen Basin, Argentina, in order to characterise the palaeoenvironmental and palaeo-climatic conditions during the deposition of this unit. Five types of palynofacies (P-l to P-5) have been identified and are interpreted to indicate a restricted marine to inner neritic environment. In P-1 and P-4, a marine environment close to the terrestrial source area with moderate oxidizing conditions and energy, is suggested. In P-2, the assemblage of freshwater algae, acritarchs and prasinophytes suggest a marginal marine environment influenced by fluvial discharge. In P-3, the marine microplankton content reflects conditions ranging from a marginal-marine (sub-normal salinity) to an inner neritic environment. In P-5, a dysoxic marine environment (probably marginal) is suggested. Warm and relatively humid (abundance of Cheirolepidiaceae in association withAraucariaceae) and locally humid (presence of swamps or ponds, on the alluvial plains) conditions are inferred. TOC content (65% of the analyzed samples reach TOC values over 1%), TAI values (2 to 2+, transitional between an immature phase and the window of liquid petroleum generation) and kerogen type (P-1, P-2 and P-5 show transitional characteristics between kerogen type II and III, while P-3 and P-4 show characteristics of kerogen type III and occasionally type IV), suggest that, in the studied area, the Los Molles Formation has some hydrocarbon potential. However, kerogen state suggests that the anoxic-dysoxic conditions of the site of deposition were not optimum for its preservation.

Palynofacies analysis of surface sediments from the Beagle Channel and its application as modern analogues for Holocene records of Tierra del Fuego, Argentina

Palynofacies analysis of surface sediments from the Beagle Channel, Tierra del Fuego, Argentina, was carried out to establish modern analogues for comparison with other Holocene marine records in southern Isla Grande de Tierra del Fuego. Our results show the dominance of highly degraded translucent phytoclasts, associated with amorphous organic matter (AOM) and palynomorphs, while opaque phytoclasts are poorly represented. The organic constituents indicate the proximity of the continental source area to marine environments, with distances and/or times of relatively short transport. The predominance of translucent phytoclasts associated with pyrite suggests reducing conditions, probably associated with marginal-marine environments. Among the terrestrial palynomorph group, the predominance of Nothofagus pollen reveals the presence of forests along the channel. The high terrestrial organic matter input to the depositional area are consistent with a marginal-marine environment. The aquatic palynomorphs, mainly dinoflagellate cysts show assemblages characterised by low species diversity and low concentration values. The dominance of Peridiniales over Gonyaulacales suggests inner neritic environments. Comparison with two fossil sections of Mid-Late Holocene age (Albufera Lanushuaia and Río Ovando) shows similar distribution of the total palynological matter.

Quantitative Analysis of Cenozoic Palynofloras from Patagonia, Southern South America

The statistical analysis of published Paleocene-Late Miocene palynological data from Patagonia supports several major stages of vegetation. These stages represent distinctive floral assemblages, both in composition and structure. Detrended correspondence analysis shows that during the Paleocene, southern South America was dominated by Australasian, Neotropical and Pantropical phytogeographical elements (Gondwanic paleoflora). The climate was warm and very humid. The Early Eocene was dominated by Neotropical and Pantropical taxa (Subtropical Gondwanic Paleoflora) and a reduced proportion of Australasian and a low proportion of Antarctic elements. The Middle Eocene and Oligocene were characterized by the ‘Mixed Paleoflora’ with the exception of the Sloggett Formation. The climate was less humid due to the onset of the Antarctic glaciation. The presence of Antarctic palynomorphs (Nothofagaceae, Podocarpaceae, Proteaceae) in Patagonia is consistent with the global cooling trend during the Late Eocene and Early Oligocene. By the Late Oligocene-Early Miocene, warm climates allowed the southward dispersal of Neotropical elements (palms, Cupania, Alchornea, Rubiaceae, Combretaceae), adding megathermal elements to the local Gondwanic floras. The appearance of some Neotropical families (Symplocaceae, Euphorbiaceae Alchornea) may indicate the Late Oligocene global warming event. The rise of xerophytic and halophytic shrubby-herbaceous elements (Convolvulaceae, Asteraceae, Poaceae, Chenopodiaceae and Ephedraceae) during the Late Oligocene, becoming more abundant during the Early Miocene began to give a modern appearance to plant communities. The Early-Middle Miocene corresponds to the Transitional Paleophytogeoprovince of central and southeastern Argentina, defined by a mix of Neotropical and Austral components. The Middle—Late Miocene was characterized by the final demise of megathermal elements in Patagonia, coupled with an increasing diversity and abundance of xerophytic adapted taxa, including Asteraceae, Chenopodiaceae and Convolvulaceae. Late Miocene vegetation was similar to the present vegetation, with the steppe expanded across extra-Andean Patagonia and the forest restricted to western areas where rainfall was still abundant.

PALINOESTRATIGRAFÍA DE LA FORMACIÓN SALTO DEL MACHO, PALEÓGENO DE LA CUENCA DE ÑIRIHUAU, ARGENTINA

Abstract. PALYNOSTRATIGRAPHY OF SALTO DEL MACHO FORMATION, PALEOGENE OF THE ÑIRIHUAU BASIN, ARGENTINA. The complete record of the palynomorphs from the Salto del Macho Formation (Paleogene) is presented from its type locality at the Foyel River section, Ñirihuau Basin Andean area, Argentina. Elements of continental and marine origin were identified: a total of 109 species corresponding to Bryophyta, Lycopodiophyta and Polypodiosida spores, Gymnospermophyta and Magnoliophyta (Angiospermae) pollen grains, continental algae and marine organic-walled microplankton. The stratigraphic distribution of sporomorphs recognized in the Salto del Macho Formation at other Paleogene—early Neogene (Miocene) basins from Patagonia argentina, Chile and Antarctica is presented. The presence of Echitriporites trianguliformis form A Müller et al., Psilatricolpites minutus González Guzmán, and Myrtaceidites parvus form nesus Cookson and Pike at the Salto del Macho Formation represents the first record of these species in Argentina. An age comprised between middle Eocene and early Oligocene is here suggested for this unit, on the basis of data yielded by palynological markers and palynostratigraphic and multivariate analyses.

Palynotaphofacies analysis applied to Jurassic marine deposits, Neuquén Basin, Argentina

Taphonomic analysis was performed on palynological samples of marine successions from the Cuyo Group of the Neuquén Basin. The group comprises the Los Molles and Lajas Formations (Middle Jurassic) and represents the first major marine depositional episode after the configuration of the basin. A total of 21 outcrop samples from five sections, located in the central-western part of the basin, were analyzed. The palynological counts of each sample were carried out taking into account the preservation state of the palynomorphs, which was mainly influenced by two parameters: their intrinsic properties and the environmental depositional conditions. Four main deterioration types (corrosion, degradation, mechanical damage, and concealment by authigenic minerals) and their six combinations were identified. The growth of pyrite crystals within the palynomorphs was strongly influenced by the exine structure, being dominant in bisaccate pollen grains. Mechanical damage appears to be the most important deterioration type, reflecting the highly dynamic conditions of shelfal marine environments. The term Palynotaphofacies (Pt) was proposed to characterize a sedimentary rock yielding palynological associations with distinctive preservational features. Three palynotaphofacies have been recognized: Pt-1 (tidal-influenced environments) is characterized by the highest percentage of deteriorated forms, reflecting either intermittent exposure to weathering or intense reworking. Pt-2 shows the highest percentage of well-preserved palynomorphs associated with rapid burial due to a high sedimentation rate and it comes from the delta-front facies of fluvial-dominated deltas. Finally, Pt-3 was identified in samples of prodelta hyperpycnites with a wide predominance of terrigenous components and it is characterized by the coexistence of well-preserved and deteriorated palynomorphs.

PALINOLOGÍA DEL MESO-CENOZOICO EN ARGENTINA. VOLUMEN EN HOMENAJE A MIRTA ELENA QUATTROCCHIO

Resumen . Este volumen esta dedicado a la Dra. Mirta Elena Quattrocchio, una de las investigadoras mas destacadas en el campo de la Palinologia a nivel nacional e internacional. Consta de ocho contribuciones, cuyas autorias corresponden a algunos de los investigadores que fueron orientados por la Dra. Mirta Quattrocchio, durante distintas etapas de su carrera. En la primera parte se incluyen tres articulos en depositos mesozoicos, uno en la provincia de Chubut y dos en la Cuenca Neuquina. En la segunda parte se incluyen cuatro trabajos realizados en depositos del Cenozoico, dos en la provincia de Buenos Aires y dos en Tierra del Fuego. La contribucion invitada sintetiza y actualiza la biocronoestratigrafia de la provincia de Buenos Aires a partir del registro de vertebrados. Abstract . This volume is dedicated to Dr. Mirta Elena Quattrocchio, one of the leading researchers in the field of Palynology. It includes eight contributions, whose authorship corresponds to some of the researchers who were oriented by Dr. Mirta Quattrocchio, during her career. The first section includes three articles from Mesozoic deposits, one in Chubut Province and two in the Neuquen Basin. The second part includes four articles associated with Cenozoic deposits, two in Buenos Aires Province and two Tierra del Fuego. The guest contribution summarizes and updates the biochronoestratigraphy of the Buenos Aires Province based on vertebrates record.