Resumen de Estudio palinológico de la perforación 201 (DI. NA. MI. GE.), Pérmico, Uruguay
- español
Se realiza el estudio palinológico de la perforación 201 (DI.NA.MI.GE.) que abarca sedimentos de las Formaciones Tres Islas y Frayle Muerto. La palinoflora hallada está compuesta principalmente por esporas de los géneros Punctatisporites y Lundbladispora. Los granos de polen están representados, fundamentalmente, por los monosacados Caheniasaccites y Plicatipollenites. Los granos estriados y bisacados son escasos. Se propone un paleoambiente caracterizado por una paleoflora pteridofítica higrófila en los niveles inferiores de la perforación. En los niveles superiores se registra mayor cantidad de componentes mesófilos. Se realiza una comparación con las zonaciones bioestratigráfica de Brasil y se propone una edad Artinskiense a Kunguriense para los sedimentos.
- English
Core DINAMIGE 201 is studied from the palynological point of view. This core comprises sediments from Tres Islas and Frayle Muerto Fms. These stratigraphic units are part of the Permian sediments of Uruguay. They arise in the surface in the Northeastern region of this country (fig. 1). They were interpreted as a delta and shelf environments, respectively.
A total amount of palynological species were found. They are mainly spores, particularly psilate triletes and cingulizonates. Among pollen grains, the most important group are the monosaccate, while the striated and bisaccate grains are very scarce. The most common genera are, among the trilete spores, Punctatisporites, Granulatisporites and Lundbladispora. The other hand, the most common pollen grains belong to the genera Caheniasaccites and Plicatipollenites.
The palynoflora found in the lower strata (up to 32 metres) is characterised by a) a variation of the dominant genus in each sampled level; and b) the almost complete absence of bisaccate and striate pollens. The samples from the upper levels have a relatively homogeneous composition, and are characterised: a) by the dominance of the genera Lundbladispora and Punctatisporites; b) by the disappearance of the genera Cristatisporites and Vallatisporites; and c) by the presence of bisaccate and striate.
This palynological assemblage was compared with the palynoflora found in the correlative formations in Brazil (Marques-Toigo & Pons, 1976; Ybert, 1975; Dias-Fabricio, 1981; Marques-Toigo et al., 1982; Marques-Toigo et al., 1984; Piccoli et al., 1985; Picarelli et al., 1987). Many features are shared with them. For instance, it can be mentioned the higher importance of the trilete spores in regard to the pollen grains, and the inverse behaviour of the sculpturing trilete spores relative to the cingulizonate spores. Also, it can be indicated that there is a high number of shared species between the bore studied here and the microflora described in the Brazilian papers.
The environment proposed for the surrounding zone of the lower levels (up to 34 metres) includes a hygrophilous pteridophytic palaeoflora (Vergel, 1986). In the upper part the palynological contents undergo a change, ie some genera of cingulizonate spores disappear and bisaccate and striate pollens appear, though in small number. This variation is coincident with a shift to finer lithologies. This is interpreted as a synchronous shift in the deposition environment to shallow bays (Andreis et al., 1991). No marine-originated material was found. In several samples, the presence of the alga genus Botryococcus was recorded.
The results were compared with the bioestratigraphic zonations from Brazil, proposed by Marques-Toigo (1988) and by Daemon & Quadros (1970). Regarding the first of them, the assemblage studied here resembles the Caheniasaccites ovatus Subzone. In connection to the second one, it is comparable with the ages H2/H3 and I-J. Therefore, an Artinskian-Kungurian age is proposed for the bearing sediments.
