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

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

FACIES

SPRINGER

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

0172-9179

Taphonomic analysis was performed on palynological samples of marine successions from the Cuyo Group of the Neuquén Basin. The group comprises the Los Molles and Lajas Formations (Middle Jurassic) and represents the first major marine depositional episode after the configuration of the basin. A total of 21 outcropsamples from five sections, located in the central-western part of the basin, were analyzed. The palynological counts of each sample were carried out taking into account the preservation state of the palynomorphs, which was mainlyinfluenced by two parameters: their intrinsic properties and the environmental depositional conditions. Four main deterioration types (corrosion, degradation, mechanical damage, and concealment by authigenic minerals) and their sixcombinations were identified. The growth of pyrite crystals within the palynomorphs was strongly influenced by the exine structure, being dominant in bisaccate pollen grains. Mechanical damage appears to be the most important deterioration type, reflecting the highly dynamic conditions of shelfal marine environments. The term Palynotaphofacies (Pt) was proposed to characterize a sedimentary rock yielding palynological associations with distinctive preservational features. Three palynotaphofacies have been recognized:Pt-1 (tidal-influenced environments) is characterized by the highest percentage of deteriorated forms, reflecting either intermittent exposure to weathering or intense reworking. Pt-2 shows the highest percentage of well-preservedpalynomorphs associated with rapid burial due to a high sedimentation rate and it comes from the delta-front facies of fluvial-dominated deltas. Finally, Pt-3 was identified in samples of prodelta hyperpycnites with a wide predominanceof terrigenous components and it is characterized by the coexistence of well-preserved and deteriorated palynomorphs.