Recent advances on the Mississippian palynostratigraphy of the Malimán Formation, northwestern Argentina

AMENÁBAR, C.R.

Bonn (Alemania)

Congreso; 12th International Palynological Congress (IPC-XII 2008) and 8th International Organisation of Palaeobotany Conference (IOPC-VIII 2008); 2008

A palynozonal scheme for the Mississippian deposits of the Malimán Formation cropping out in northwestern Argentina is established based on extensive palynological studies on three localities. The unit was accumulated in marine, littoral and fluvial-deltaic environments. Samples yielded regular to well-preserved palynomorphs composed of 114 spore species and scarce microplankton. Recycled Devonian taxa are quite common in the samples, and they mainly derived from the underlying Chigua Formation. Three assemblage zones were established from oldest to youngest: Palynozone 1. Characterized by the first occurrence of Convolutispora insulosa, C. varicosa, C. sp. cf. C. usitata, Crassispora invicta, C. trychera, Dibolisporites sp. cf. D. setigerus, Emphanisporites hibernicus, Grandispora debilis, G. notensis, G. spiculifera and Verrucosisporites oppressus, among others. All of them, exclusive from this zone, disappeared in the upper limit with the subsequent zone. Quantitatively this assemblage is distinguished by a high content of specimens of a new species of Crassispora. This zone is recognized in the lowermost part of the unit. Palynozone 2. The lower limit is defined by the appearance of two key species, Schopfites claviger and Colatisportes decorus and most of the species of Verrucosisporites (V. congestus, V. morulatus, V. papulosus and V. baccatus) are also recorded in this zone. Apiculatisporis castanea and A. variocorneous are exclusive of this zone and species of Crassispora and Cristatiporites are present in a low proportion. This zone is mainly represented in the middle part of the Malimán Formation. Palynozone 3. The lower limit is marked by the dominance of species of Cristatisporites (e.g. C. indolatus, C. inordinatus) and Densosporites is also a common genera. The upper limit is defined by the uppermost palyniferous sample located at the beginning of the deltaic deposits of the upper part of the unit while the rest of this section is barren due to its predominantly coarse-grained lithology. Based on the stratigraphic ranges of the species identified, the limit between the first and second palynozones is likely latest Tournaisian-earliest Viséan and the third one is early Viséan. A correlation of these palynozones is proposed with the Viséan Anapiculatisporites largus of Australia, the late Tournaisian-early Viséan CM and Pu Zones of Euramerica and the early Viséan assemblage of the Itacua Formation of Bolivia.