Late Jurassic microforaminiferal linings from the Neuquén Basin, Argentina.

VOLKHEIMER, W. & ZAVATTIERI, A.M.

Mendoza, Argentina

Simposio; III Simposio Argentino del Jurásico; 2007

Asociación Geológica Argentina

In nearcoast environments of the Late Jurassic (Tithonian) Picún Leufú Formation, large proportions of microforaminiferal linings occur in association with marine dinoflagellate cysts, acritarchs, prasinophytes and terrestrial species of palynomorphs. Microforams have been largely ignored in earlier contributions on the palynology of the Neuquén Basin, due to their scarce representation. In the middle part of the Picún Leufú Formation at its type locality there occur several morphotypes, ranging from uniserial to biserial, coiled planispiral and coiled trochospiral morphotypes. No form genera and species of microforams are distinguished in this contribution, as there do not exist sufficient published data on the relationship between the foraminiferal tests and their linings. Instead, we preferred to use informal groupings as an interim solution. The most frequent dinocysts associated are Ctenidodinium tenellum, Hystrichosphaerina neuquina, Sentusidinium sp. A, Batiacasphaera sp., Meiourogonyaulax sp., Gonyaulacysta spp., Systematophora sp. A and Pareodinia sp. The acritarchs Baltisphaeridium sp. and Micrhystridium lymensis var. gliscum and the prasinophytes Leiosphaeridia staplinii and Leiosphaeridia hyalina are common. Frequent terrestrial species of the palynoflora are Callialasporites dampieri, C. trilobatus, C. segmentatus, C. microvelatus, C. turbatus, Classopollis simplex, Classopollis classoides, Alisporites sp., Leptolepidites spp. and several types of cingulate trilete spores. In one extreme case of the studied levels, microforams constitute up to 32% of the total spectrum of palynomorphs, followed by dinoflagellate cysts (24%), prasinophytes (12%) and acritarchs (4%), associated with 28% of terrestrial species of the palynoflora. In this special case the t / m-index (relation between terrestrial and marine species of the palynobiota) is 0.39.Ctenidodinium tenellum, Hystrichosphaerina neuquina, Sentusidinium sp. A, Batiacasphaera sp., Meiourogonyaulax sp., Gonyaulacysta spp., Systematophora sp. A and Pareodinia sp. The acritarchs Baltisphaeridium sp. and Micrhystridium lymensis var. gliscum and the prasinophytes Leiosphaeridia staplinii and Leiosphaeridia hyalina are common. Frequent terrestrial species of the palynoflora are Callialasporites dampieri, C. trilobatus, C. segmentatus, C. microvelatus, C. turbatus, Classopollis simplex, Classopollis classoides, Alisporites sp., Leptolepidites spp. and several types of cingulate trilete spores. In one extreme case of the studied levels, microforams constitute up to 32% of the total spectrum of palynomorphs, followed by dinoflagellate cysts (24%), prasinophytes (12%) and acritarchs (4%), associated with 28% of terrestrial species of the palynoflora. In this special case the t / m-index (relation between terrestrial and marine species of the palynobiota) is 0.39.