Alluvial-aeolian facies interaction and basin architecture in the Tordillo Fm., Upper Jurassic, northern Neuquén Basin (Argentina): An approach for paleogeographic and tectonic development

J.LÓPEZ GÓMEZ; PALMA, R.M; J. MARTÍN-CHIVELET

Congreso; 28th IAS Meeting of Sedimentology; 2011

The Neuquén Basin is a Mesozoic back-arc basin located in central-western Argentina and eastern Chile and present-day incorporated into the Andean retro-arc foreland basin. In the northern sector of that basin, the Kimmeridgian - lowermost Tithonian (Upper Jurassic) Tordillo Formation consists of continental clastic sequences deposited in an interval of generalized subsidence but showing a clear influence of fault activity, probably recurrent  from a Late Triassic-Early Jurassic rifting phase. Lower and upper contacts of this unit are sharp with the Auquilco Fm. (evaporites) and Vaca Muerta Fm. (open marine carbonates and marls) respectively.           Seven complete sections of the Tordillo Fm. have been studied in detail in the study area, from south to north: Quebrada de Leiva, Loncoche, Lagunilla, Cañada Ancha, Arroyo Felipe, Arroyo Blanco and La yesera.  Main lithofacies, architectural elements, and bounding surfaces of different order were differentiated, and their lateral and vertical stratigraphic patterns recognized and genetically interpreted.  This results in the identification of a multi-stage suite of fluvial-aeolian, heterolithic sequences, occasionally punctuated by volcaniclastic intercalations. All these deposits were generated under semiarid to arid climatic conditions.             Fluvial sedimentation was mainly related to braided systems that probably went through tectonically confined areas, where floodplains deposits were difficult to develop and preserve. Interfingering of fluvial and aeolian sediments shows clearly differentiated belts of both coexisting environments. Volcaniclastic beds are mainly andesitic in composition with presence of subaerial pyroclastic flows and fallout deposits. They are massive or show sequences of reverse, normal and normal-reverse grading in which traction structures as lamination and cross-bedding appear.           The studied sections are transversally oriented to the main axis of the northern Neuquén Basin and record the tectonic, paleogeographic and sedimentary evolution of the area. This evolution suggests an active tectonism during sedimentation, still near the end of the Jurassic, as well as a noticeable influence of magmatic activity, which could also cause important regional uplift and later subsidence.     Acknowledgements: This is a contribution to projects PIP 0564 (CONICET), UBACyT X-476 (Universidad de Buenos Aires), and Research Groups 910198 and 910429 (UCM-Comunidad de Madrid, Spain).