Palaeoenvironments and palaeoclimate of the uppermost Cuyo Group and lowermost Lotena Group at Quebrada Álvarez, Picún Leufú Sub-basin, Patagonia, Argentina: a preliminary study based on palynology

AbstractThe palynological (palynostratigraphical/palynofacies) analysis of samples from the Middle Jurassic outcrop at the Quebrada Álvarez section located in the Neuquén Basin, Patagonia, Argentina, allowed us to begin to evaluate the palaeoecological significance of the recovered palynofloras and their importance in the evolution of these ecosystems, during the transition between the uppermost Cuyo Group and the lowermost Lotena Group. The Lajas Formation, characterised by the palynofacies type A, could be interpreted as tide-modified delta front environment. The high abundance and diversity of the palynomorphs identified in the studied samples, contribute to improve the palynological knowledge of the Challacó Formation (palynofacies type B–F). Considering the palaeoecological requirements of the recognised plant families, relatively humid and warm climate conditions could be inferred during the deposition of this unit. Also, the “seasonally dry (winterwet)” biome (Rees et al. 2000) was interpreted for the first time in the Neuquén Basin. Based on selected key taxa a Late Bathonian–early Callovian age is proposed for the Challacó Formation at the Quebrada Álvarez section. The palynological matter recorded in this unit suggests the development of a lacustrine environment with cycles of relative contraction and expansion of the water body due to fluctuations between relatively dry and wet conditions. The dominance of phytoclasts, mainly opaque particles, and freshwater algae (Botryococcus) in the Bosque Petrificado Formation (palynofacies type G–I) could suggest the development of a freshwater to brackish lacustrine environment. Based on the dominance of the same group of palynomorphs (Chlorophyta algae) in the Challacó and Bosque Petrificado formations, similar palaeoenvironmental conditions would be inferred for these units. From a lithofacies analysis point of view, the Challacó and Bosque Petrificado formations show isopic facies associations in the study locality.Key words: Lajas FormationChallacó FormationBosque Petrificado FormationMiddle JurassicNeuquén BasinArgentinaDisclaimerAs a service to authors and researchers we are providing this version of an accepted manuscript (AM). Copyediting, typesetting, and review of the resulting proofs will be undertaken on this manuscript before final publication of the Version of Record (VoR). During production and pre-press, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal relate to these versions also. AcknowledgmentsThe authors thank Dr. Rosemary Scoffield for her critical reading of the manuscript. We thank Dr. James Riding (Managing Editor), Dr. Sofie Lindström and an anonymous reviewer for their helpful suggestions which improved the final version of the manuscript. The authors kindly acknowledge to Dr. Germán Otharán and Dr. Ainara Irastorza for the field work and the stratigraphical column.Disclosure statementNo potential conflict of interest was reported by the authorsTable 1. Classification of the palynological matter with source affinity indications.Download CSVDisplay TableTable 2. List of the identified palynomorph species of the Challacó and Bosque Petrificado formations at the Quebrada Álvarez section. Botanical affinities of spores, pollen and organic-walled microplankton from the units. Principal source of information concerning the natural relationships of dispersed palynomorphs, based on Dettmann (1963), Filatoff (1975), de Jersey and Raine (1990), Balme (1995), Sajjadi and Playford (2002a, 2002b), McKellar (1998), Schrank (2010) and Martínez et al. (2008).Download CSVDisplay TableTable 3. Classification of the spore and pollen genus recorded in the present study and considered to be characteristic of palaeoenvironments and palaeoclimates. Principal source of environment and climatic inferences: Zalessky (1926), Wilde (1989), Yi et al. (1993), Tyson (1995), Batten and Grenfell (1996), Abbink (2004), Coiffard et al. (2007), Schrank (2010), Kuajú et al. (2013), Matheus et al. (2013), Stukins et al. (2013), Li et al. (2014), Olivera et al. (2015), Lindström et al. (2017), Jurkowska et al. (2019), Mostafa and Lofty (2020), Barua et al. (2021).Download CSVDisplay TablePlate 1. Selected palynomorphs and palynofacies type recognised in samples at the Quebrada Álvarez section. Scale bars: 10 µm. Lajas Formation: 1. Equidimensional opaque phytoclasts (palynofacies type A) sample UNSP-QA5867, EF: Y43. Challacó Formation: 2. Translucent phytoclasts (palynofacies type B) sample UNSP-QA5876, EF: U28. 3. Granular AOM (palynofacies type C), sample UNSP-QA5872, EF: F27/1. 4. Equidimensional opaque phytoclasts (palynofacies type D), sample UNSP-QA5878, EF: G44/3.5. Palynomorphs (palynofacies type E) sample UNSP-QA5874, EF: U34/1.6. Opaque phytoclasts (palynofacies type F), sample UNSP-QA5875, EF: R43/1. Bosque Petrificado Formation: 7. Granular AOM (palynofacies type G), sample UNSP-QA5882, EF: O41/4. 8. Translucent and opaque phytoclasts (palynofacies type H1). 9. AOM (palynofacies type H2), sample UNSP-QA5880, EF: O16. 10–12. Botryococcus at transmitted light (11–12) and at UV light (11; palynofacies type I).Display full sizePlate 2. Selected palynomorphs recorded in samples at the Quebrada Álvarez section. Scale bars: 10 µm. 1. Deltoidospora minor sample UNSP-QA5874, EF: Y17/3. 2. Dictyophilidites harrisi sample: UNSP-QA5874, EF: Y42/2. 3. Cibotiumspora jurienensis sample UNSP-QA5874, EF: Y18/3. 4. Concavisporites laticrassus, sample UNSP-QA5874, EF: Y20/3. 5. Antulsporites saevus sample UNSP-QA5876, EF: U49. 6. Verrucosisporites varians, sample UNSP-QA5874, EF: Y34. 7. Osmundacidites araucanus sample: UNSP-QA5874, EF: O36/4. 8. Peroaletes ieiunus sample UNSP-QA5874, EF: T49/1. 9. Callialasporites dampieri sample UNSP-QA5874, EF: Y32. 10. Vitreisporites pallidus sample UNSP-QA5874, EF: Y34. 11. Copepod egg sample UNSP-QA5870, EF: L40/3.12. Alisporites similis sample UNSP-QA5874, EF: X23/2. 13. Ovoidites tripartitus sample UNSP-QA5873, EF: Y25/2. 14–19. Botryococcus sp. cf. B. braunii transmitted and UV light, 14–15. Sample UNSP-QA5877, EF: V38/2; 16–17. Sample UNSP-QA5872, EF: D38/2; 18–19. Sample UNSP-QA5872, EF: L36/4.Display full sizePlate 3. Selected palynomorphs recorded in samples at the Quebrada Álvarez section. Scale bars: 10 µm. 1–8. Leiosphaeridia sp. transmitted and UV light, 1–2. Sample UNSP-QA5877b, EF: P21. 3–4. Sample UNSP-QA5873, EF: Y19/2. 5–6. Sample UNSP-QA5873, EF: Y25/2. 7–8. Sample UNSP-QA5877, EF: G25/1.Display full sizeFigure 1. A. Upper right box shows Neuquén Basin location in South America. B. Geologic map of the basin showing location of the Quebrada Álvarez section (black rectangle). C. Stratigraphical column of the Neuquén Basin. Left: units in the Northern-central basin. Right: units in the Picún Leufú Sub basin (South).Display full sizeFigure 2. Stratigraphical Quebrada Álvarez section showing sedimentological and fossil characteristics of the units, and location of the palynological samples and palynofacies types (PT). Numbering is an abbreviation of samples catalogue nomenclature.Display full sizeFigure 3. Quantitative distribution of the degree of preservation (High, Moderate and Low) of the Botryococcus colonies in the samples studied of the Challacó and Bosque Petrificado formations at the Quebrada Álvarez. All right pie charts show the percentages of simple vs. compound colonies per sample.Display full sizeFigure 4. Cluster analysis, using Euclidean distance and the unweighted pair group method (UPGM), showing the grouping of the identified palynofacies type in the Challacó Formation.Display full sizeFigure 5. Cluster analysis, using Euclidean distance and the unweighted pair group method (UPGM), showing the grouping of the identified palynofacies type in the Bosque Petrificado Formation.Display full sizeFigure 6. Relative frequency distribution of the different recognised categories of palynological matter based on the total count of 500 particles per sample in the Lajas (white), Challacó (purple to blue) and Bosque Petrificado (grey to black) formations, Quebrada Álvarez section. AOM: Amorphous organic matter.Display full sizeFigure 7. A. Quantitative distribution of major palynological matter groups in the Challacó Formation, Quebrada Álvarez locality. B. Pie chart reflecting the quantitative distribution of major palynomorph groups expressed in percentages of total palynomorph accounts.Display full sizeFigure 8. A. Relative frequency distribution of major palynomorph groups in the Challacó Formation at the Quebrada Álvarez section, expressed in percentages of total palynoflora. B. Relative frequency distribution of the major palynomorph groups identified in the Bosque Petrificado Formation.Display full sizeFigure 9. Reconstruction of palaeoenvironmental conditions during the deposition of the Challacó Formation according to the palynomorph content. A. Humid season. Circle showing the main groups of palynological matter (phytoclasts, trilete spores, caytoniacean pollen grains and freshwater algae). B. Dry season. Circle showing the main groups of palynological matter (AOM and freshwater algae).Display full sizeFigure 10. Range chart of key species from samples of the Challacó Formation at the Quebrada Álvarez section. The black bars indicate the worldwide distribution and the red bars indicate the Argentinian distribution of these taxa. The green column indicates the more probably age of the Challacó Formation at the locality studied.Display full sizeAdditional informationFundingThis work was supported by the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) [under Grant PIP 11220200101514CO] and the Secretaría General de Ciencia y Tecnología of Universidad Nacional del Sur (SEGCyT) [under Grant PGI 24/H156].Notes on contributorsAmira Celeste ChalabeAMIRA C. CHALABE is a doctoral fellow at the Consejo Nacional de Investigaciones Científicas y Técnicas (INGEOSUR-CONICET) in Bahía Blanca, Argentina. She obtained a B.S. in geology during 2019 from the Universidad Nacional del Sur. Amirás current research interests include the Palynofacies and palynostratigraphy of the Mesozoic of Argentina.Daniela Elizabeth OliveraDANIELA E. OLIVERA is a researcher at the Consejo Nacional de Investigaciones Científicas y Técnicas (CCT-CONICET) in Bahía Blanca, Argentina and is also a teaching assistant in palaeontology at the Universidad Nacional del Sur, Bahía Blanca, Argentina. Daniela’s research interests include palynofacies analysis and the palynostratigraphy of Argentinian Mesozoic and Cenozoic successions.Marcelo Adrián MartínezMARCELO A. MARTÍNEZ is a research scientist at the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and a professor at the Geology Department of the Universidad Nacional del Sur (UNS), Bahía Blanca, Argentina. He received his Ph.D. in Geology in 1999 from the Universidad Nacional del Sur, Argentina. Marcelo’s research has focused on palynofacies analysis and the palynostratigraphy of Argentinian Mesozoic and Cenozoic sedimentary sequences.Carlos ZavalaCARLOS ZAVALA is a professor at the Geology Department of the Universidad Nacional del Sur (UNS), Bahía Blanca, Argentina. He has extensive experience in sedimentology, stratigraphy, and basin analysis of sequences spanning from the Paleozoic to the Quaternary. His current research focuses on the understanding of sediment gravity flow deposits, both sandy and muddy, and their significance as reservoir and source rocks.