Environmental and climatic proxies for the Cañadón Asfalto and Neuquén basins (Patagonia, Argentina): review of Middle to Upper Jurassic continental and near coastal sequences

Abstract

-In this review, we include several proxies (sedimentology, palynology, invertebrates) from the Cañadón Asfalto and Neuquén basins, to infer the environments and regional climatic context during the Middle to Late Jurassic of Patagonia. In central Patagonia, early in the Middle Jurassic, and associated with a magmatic arc, began the sedimentary fi lling of Jurassic continental sub-basins in the Cañadón Asfalto Basin. Lacustrine and fl uvio-deltaic sediments, bearing a continental Middle Jurassic palynobiota, correspond to the Las Chacritas Member, while the sediments and palynobiota from the Late Jurassic Puesto Almada Member (both in the Cañadón Asfalto Formation) indicate a palustrine wetland subenvironment immersed within an arid macroenvironment. Paleoinvertebrates (conchostracans and sponges) of this formation suggest wet-dry cycles in the water bodies they inhabited. The sedimentological information together with the continental and coastal palynomorph assemblages of the back arc Neuquén Basin, allowed distinguishing a complete regressive-transgressive sequence for the Middle Jurassic Lajas Formation. For the Upper Jurassic in this basin, the thick gypsum and anhydrite deposits of the evaporitic coastal Auquilco Formation correlate with extended deposits of eolian sandstones corresponding to the Botucatú paleodesert, and a saltmarsh environment is inferred from the palynofl ora. The palynologic associations from both basins indicate a regional warm climate with seasonal aridity. Climatic conditions would have been drier in the continental interior (Cañadón Asfalto Basin), with strongly seasonally distributed temperatures, and moister in the western coast of the continent (Neuquén Basin), during the marine transgressions.Key words: paleoenvironment, paleoclimate, Jurassic, Cañadón Asfalto Basin, Neuquén Basin, Argentina.RESUMO -Na presente revisão foram incluídos vários proxies (sedimentologia, palinologia, invertebrados), das bacias de Cañadón Asfalto e Neuquén, para inferir o contexto climático regional e ambiental durante o Jurássico Médio e Superior da Patagônia. Na região central da Patagônia, no início do Jurássico Médio, e associado a um arco magmático, começou o preenchimento sedimentar de sub-bacias continentais jurássicas na bacia Cañadón Asfalto. Os sedimentos fl úvio-deitaico e lacustres, tendo uma palinobiota continental do Jurássico Médio correspondente ao Membro Las Chacritas, enquanto os sedimentos e a palinobiota do Jurássico Superior do Membro Puesto Almada (ambos na Formação Cañadón Asfalto) indicam um subambiente palustre úmido imerso em um macroambiente árido. Os paleoinvertebrados (conchostráceos e esponjas) desta formação sugerem ciclos úmidos-secos nos corpos de água por eles habitados. A informação sedimentológica juntamente com 72

The palynology of the Cañadón Asfalto Formation (Jurassic), Cerro Cóndor depocentre, Cañadón Asfalto Basin, Patagonia, Argentina: palaeoecology and palaeoclimate based on ecogroup analysis

“…The earliest palynological studies on the Cañad on Asfalto Formation in the study area were carried out by Volkheimer (1971), P€ othe de Baldis (in Nullo & Proserpio 1975) and Volkheimer et al (2001Volkheimer et al ( , 2008. Volkheimer et al (2008) proposed a Middle Jurassic age (latest Early Bajocian to Early Bathonian) for a palynological assemblage recognised in the Lahuinc o creek (Figure 1).…”

Jurassic Palynology from “The Dinosaur Coast” of Asturias (Lastres Fm., Northwestern Spain): Palynostratigraphical and Palaeoecological Insights

“…Classopollis , is a pollen commonly related to tree-size conifers belonging to the Cheirolepidiaceae family, that show xerophytic and halophytic adaptations inhabiting disturbed environments as they are coastal areas [ 52 , 55 ]. In particular, Volkheimer et al [ 60 ] considered Classopollis from the Lajas Formation in the Middle Jurassic of the Neuquén Basin (Argentina) as a thermophilic coastal proxy related to extraordinary flooding in well-drained soils of the delta plain.…”

The Cretaceous Period of Weather Similar to the Present One and Its Diverse “Conchostracan” Fauna

“…The Cañadón Calcáreo Fm. (Upper Jurassic -Lower Cretaceous) was referred by [11] to sequences represented swampy areas, with a rich and diverse conchostracan fauna in subtropical seasonal dry climate. In Brazil-Uruguay the units are, the Botucatu Fm = Tacuarembó Fm (Late Jurassic -Early Cretaceous), indicating desert climate [12].…”