Sedimentary facies and palynofacies assemblages in an Eocene perennial lake, Lumbrera formation, northwest Argentina

Abstract

The combined application of sedimentary facies and palynofacies analyses constitutes a valuable method for paleoenvironmental and paleoclimatic reconstructions, especially in continental strata in which fossil information is scarce or absent. In this paper, we present an integrated model based on this methodology for the Eocene lacustrine rocks of the Lumbrera Formation in northwest Argentina. The new data contribute to the understanding of the evolution of the final post-rift stage of the Salta Group in northwest Argentina. The lacustrine deposits of the Lumbrera Formation are named Faja Verde I and Faja Verde II. In the Alemanı́a area, the Faja Verde II consists of green claystones and mudstones interbedded with sandstones and deposited in a perennial lake and fluvio-dominated delta complex. In addition, there are two major cycles that are separated by a flooding surface. The basal cycle is a retrogradational parasequence set, and the upper cycle is a progradational parasequence set. The palynofacies analysis and organic matter analytical data (TOC and Pyrolysis Rock-Eval) of each sedimentary facies are closely related to 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) subenvironments are differentiated. Each is characterized by a definitive relationship of phytoclasts, amorphous, palynomorphs, fluorescence index, quality, and quantity of the organic matter. The variation of occurrence of the Pediastrum– Botryococcus algae reflects fluctuations in the level of water related to identified cycles of shallowing.