Sedimentary facies and palynofacies assemblage in Eocene perennial lake, Lumbrera Formation, northwest Argentina

DEL PAPA, C; GARCÍA, V.; QUATTROCCHIO, M.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

Elsevier

Año: 2002 vol. 15 p. 553 - 569

0895-9811

The combined application of sedimentary facies and palynofacies analysis constitutes a valuable method in the paleoenvironmental and paleoclimatic reconstruction, specially in continental strata where the fossil information is scarce or absent. Furthermore provides a good tool in the sequence stratigraphy analysis of lacustrine basins. In this paper we present an integrated model based on this methodology utilized in the Eocene lacustrine rocks of Lumbrera Formation in the northwest of Argentina. Finally the new data contribute with the general understanding of the evolution of the final post-rift stage of the Salta Group in the northwest Argentina. The lacustrine deposits of Lumbrera Formation are named Faja Verde I and Faja Verde II. In the Alemanía area, the Faja Verde II consists of green claystones and mudstones interbedded with sandstones, deposited in a perennial lake and fluvio-dominated delta complex. Two major cycles separated by a flooding surface were recognized. The basal cycle is composed of a retrogradational parasequence set and the upper one is a progradational parasequence set. The palynofacies analysis and the organic matter analytical data (TOC and Pyrolysis Rock-Eval) of each sedimentary facies are in close relationship with the dynamics of the depositional environment. Proximal prodelta (Palynofacies association I), Distal prodelta (Palynofacies association II), Lacustrine (Palynofacies association III) and Interdistributary bay fill (Palynofacies association IV) sub-environments were differentiated. Each one is characterized by a definitive relationship of phytoclasts, amorphous, palynomorphs, fluorescence index, quality and quantity of the organic matter.It has been observed that the variation of occurrence of the Pediastrum – Botryococcus algae reflects fluctuations in the level of water related to identified cycles of shallowing.