Palynotaphofacies analysis applied to Jurassic marine deposits, Neuquén Basin, Argentina

MARTÍNEZ, M.A.; OLIVERA, D.; ZAVALA, C.A.; QUATTROCCHIO, M.E.

FACIES

SPRINGER

Lugar: Berlin; Año: 2016 vol. 62 p. 1 - 16

0172-9179

Taphonomic analysis was performed onpalynological samples of marine successions from theCuyo Group of the Neuquén Basin. The group comprisesthe Los Molles and Lajas Formations (Middle Jurassic)and represents the first major marine depositional episodeafter the configuration of the basin. A total of 21 outcropsamples from five sections, located in the central-westernpart of the basin, were analyzed. The palynological countsof each sample were carried out taking into account thepreservation state of the palynomorphs, which was mainlyinfluenced by two parameters: their intrinsic properties andthe environmental depositional conditions. Four main deteriorationtypes (corrosion, degradation, mechanical damage,and concealment by authigenic minerals) and their sixcombinations were identified. The growth of pyrite crystalswithin the palynomorphs was strongly influenced by theexine structure, being dominant in bisaccate pollen grains.Mechanical damage appears to be the most important deteriorationtype, reflecting the highly dynamic conditions of shelfal marine environments. The term Palynotaphofacies(Pt) was proposed to characterize a sedimentary rock yieldingpalynological associations with distinctive preservationalfeatures. Three palynotaphofacies have been recognized:Pt-1 (tidal-influenced environments) is characterizedby the highest percentage of deteriorated forms, reflectingeither intermittent exposure to weathering or intensereworking. Pt-2 shows the highest percentage of well-preservedpalynomorphs associated with rapid burial due to ahigh sedimentation rate and it comes from the delta-frontfacies of fluvial-dominated deltas. Finally, Pt-3 was identifiedin samples of prodelta hyperpycnites with a wide predominanceof terrigenous components and it is characterizedby the coexistence of well-preserved and deterioratedpalynomorphs.