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

Abstract

The 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 a 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 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 material 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 (chlorophyte 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.

Keywords:

• Biostratigraphy
• Lajas Formation
• Challacó Formation
• Bosque Petrificado Formation
• Palynofacies
• Middle Jurassic
• Neuquén Basin
• Argentina

Acknowledgments

The 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 Dr. Germán Otharán and Dr. Ainara Irastorza for the fieldwork and the stratigraphical column.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) and the Secretaría General de Ciencia y Tecnología of Universidad Nacional del Sur (SEGCyT).

Notes on contributors

Amira Celeste Chalabe

AMIRA 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. Amira's current research interests include the palynofacies and palynostratigraphy of the Mesozoic of Argentina.

Daniela Elizabeth Olivera

DANIELA 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 Martínez

MARCELO 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 Zavala

CARLOS 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 Palaeozoic 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.