Palynofloras of the Chigua (Devonian) and Malimán (Mississippian) formations from the Precordillera Argentina: age, correlation and discussion of the D/C boundary

AMENÁBAR, C.R., DI PASQUO, M.M., AZCUY, C.L.

REVISTA ESPANOLA DE MICROPALEONTOLOGIA

Instituto Geológico y Minero de España

Lugar: Madrid; Año: 2009 vol. 41 p. 217 - 240

0556-655X

A qualitative and quantitative analysis is presented of palynological assemblages recovered from outcrops of the Chigua (Devonian) and Malimán (Mississippian) formations, in the Río Blanco Basin, Precordillera of Argentina. An angular unconformity separates these two formations. Both units are dated precisely in comparison with palynofloras elsewhere. The Chigua Formation is correlatable with the early Givetian G. lemurata-C. magnificus Zone of Euramerica. The stratigraphic ranges of the non-reworked taxa in the Malimán Formation support an early Viséan age. However, the presence of some late Tournaisian species suggests that the lower part of the formation correspond to this age. The palynoflora of the Malimán Formation suggests correlation with 1) the Viséan Endoculeospora larga Formation support an early Viséan age. However, the presence of some late Tournaisian species suggests that the lower part of the formation correspond to this age. The palynoflora of the Malimán Formation suggests correlation with 1) the Viséan Endoculeospora larga G. lemurata-C. magnificus Zone of Euramerica. The stratigraphic ranges of the non-reworked taxa in the Malimán Formation support an early Viséan age. However, the presence of some late Tournaisian species suggests that the lower part of the formation correspond to this age. The palynoflora of the Malimán Formation suggests correlation with 1) the Viséan Endoculeospora largaEndoculeospora larga Assemblage of Australia, 2) the late Tournaisian – early Viséan CM and Pu zones of Euramerica, and 3) the early Viséan assemblage of the Itacua Formation of southernmost Bolivia. A hiatus comprising Frasnian to early Tournaisian is confirmed on the basis of the different ages of the two assemblages and the stratigraphic ranges of reworked palynomorphs found in the Malimán Formation. These, attest to sedimentation and subsequent erosion of Frasnian and probably also Tournaisian strata. The absence of reworked forms of the latest Devonian (late Famennian or “Strunian”) suggests a corresponding period of non-deposition. The Malimán Formation also contains reworked palynomorphs of Late Silurian and Early Devonian ages. The reworking of palynomorphs documents the penecontemporaneous erosion of uplifted areas that would have conformed the Protoprecordillera, due to late Frasnian, Famennian and early Tournaisian tectonic and glacio-eustatic processes affecting the area involved.