Biomarkers in Source Rocks from Barreirinha Formation (Devonian): Distribution and Paleoenvironment Significance

Andrenilton Silva,Artur Barros,Daniel Jarvie,Alexandre De Souza,Alek Sousa,Ailton Brito,Sebastian Calderón,Afonso Nogueira,Sidney De Lima

doi:10.21577/0103-5053.20210156

Abstract

The Barreirinha Formation-Upper Devonian, is the main petroleum source rock of the Amazon Basin, deposited during the great Devonian Transgression, contributing to significant accumulations of organic matter (OM) in anoxic conditions, which allowed its preservation. The present work had the objective of characterizing the molecular composition of biomarkers in outcrops samples of the Barreirinha Formation, aiming to evaluate the paleoenvironment, thermal evolution, and the preservation of OM total organic carbon (TOC) and Rock-Eval pyrolysis indicate considerable amounts of immature OM deposited in a low oxygenation environment. Gas chromatographymass spectrometry (GC-MS) and gas chromatography-tandem mass spectrometry (GC-MS/MS) data corroborate that the OM was deposited in a suboxic to the oxic environment and low salinity (absence or low relative abundance of β-carotane and gammacerane). 24-N-Propyl-cholestane was detected and identified by synthetic pattern co-injection. High concentrations of tetracyclic polyprenoids (TPPs) in ascending order from base to top, high hopane/sterane ratios, to suggest that the samples had a high molecular weight n-alkanes, C29 steranes, low thermal evolution, and anoxic depositional paleoenvironment.

Highlights

The graytoblack shales of the Barreirinha Formation record the highest marine incursion in the western portion of the Gondwana continent.[1,2] The marine flood from the Tethys Ocean began in the Mesodevonian and entered the Amazon Basin through the Marajó Island region.[3]
The purpose of this work is the use of classical chromatographic techniques to study the geochemical biomarkers that help in understanding the sedimentation environment, redox conditions, types of organisms that contributed to deposited organic matter (OM), as well as sequence sedimentary geology of outcrop samples from the Barreirinha Formation (Devonian-Amazon Basin), collected at the southeastern edge of the Basin
The dominance of quartz within the clay particles framework suggests sedimentary material of continental origin possibly related to the continuous fluvial input attested by the upward increase of sand material (Figure 2).[17,18,19,20,21]

Summary

Introduction

The graytoblack shales of the Barreirinha Formation record the highest marine incursion in the western portion of the Gondwana continent.[1,2] The marine flood from the Tethys Ocean began in the Mesodevonian and entered the Amazon Basin through the Marajó Island region.[3] This maximum flood left a record of thick coarsening upward succession of highly radioactive organic-rich black shales, gray shale, siltstone, and sandstone.[4,5]. Previous studies have shown that organic carbon content can reach up to 10%.2. Commercial oil accumulations were identified during the 1950s, as well as large evaporite reserves that remain unexplored in the subsurface, and gas reserves discovered near the capital Manaus.[6] The geochemical characterization of the source rocks of the Amazon Basin, mainly through biomarkers, is of great relevance to understanding the deposition environment, quality and content of organic matter, and generating potential evaluation

Objectives

Results

Conclusion