Palynofacies and biomarker analysis of the lowermost Permo–Carboniferous Pular Formation, a volcanic arc sequence in the Sierra de Almeida, Northern Chile

Abstract

Palynofacies and molecular organic geochemical analyses indicate a probable lacustrine origin for three organic-rich black shale samples from the lowermost Pular Formation (Permo–Carboniferous) of northern Chile. The three samples examined exhibit high values for total organic carbon and hydrogen indices. Biomarkers and stable carbon isotopic compositions (−36.5 to −35.5‰) are typical for oil-prone type I organic matter associated with lacustrine source rocks and derived oils. Amorphous kerogen dominates the samples, and two distinct palynofacies can be recognized. The palynofacies can be visually distinguished by the presence/absence of petrofilaments, presence/absence of terrestrial organic material, and weak versus strong fluorescence. These organic facies can also be separated using hydrogen indices, the abundance of n-C 24+ paraffins, sterane (C 27, C 28, C 29) patterns, and the relative amounts of perhydro-β-carotene.