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

CHALABE, AMIRA CELESTE; OLIVERA, DANIELA E.; MARTÍNEZ, MARCELO A.; ZAVALA, CARLOS A.

PALYNOLOGY

AMER ASSOC STRATIGRAPHIC PALYNOLOGISTS FOUNDATION

Lugar: New York; Año: 2024 p. 1 - 19

0191-6122

The palynological (palynostratigraphic/palynofacies) analysis of the Middle Jurassic outcrop samples at Quebrada Álvarez section allowed to interpret the paleoenvironmental and paleoclimatic evolution during the transition of the uppermost Cuyo Group and the lowermost Lotena Group. The Lajas Formation, characterized by palynofacies type A, is interpreted as tide-modified delta front environment. Besides, the high percentages of palynomorphs identified in this contribution increase the palynological knowledge of the Challacó Formation (palynofacies type BF). Considering the paleoecological requirements of the recognized plant families, relatively humid and warm climate conditions were 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 matter (PM) registered 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 Bosque Petrificado Formation (palynofacies type GI) suggests the development of a brackish lacustrine environment. So, based on the dominance of the same group of palynomorphs (Chlorophyta algae) in the Challacó and Bosque Petrificado formations, similar paleoenvironmental conditions are inferred for these units. So, from a lithofacies analysis viewpoint the Challacó and Bosque Petrificado formations show isopic facies associations in the study locality.