Skip to Main content Skip to Navigation
Conference papers

ORBITAL FORCING OF ORGANIC MATTER QUALITY AND QUANTITY IN A SOURCE-ROCK FORMATION: THE CASE OF THE VACA MUERTA FORMATION, TITHONIAN-VALANGINIAN, NEUQUÉN BASIN, ARGENTINA

Abstract : The Vaca Muerta Formation (Jurassic-Cretaceous transition) from the Neuquén Basin is an important petroleum source-rock formation in Argentina. Several cores from exploration wells were fully analysed. A cyclostratigraphic study was also successfully conducted, based on a set of continuous data from several neighbour cored wells. Among various variables successfully tested, the Total Organic Content (TOC), either continuously measured with the Laser Induced Pyrolysis System (LIPS) method (1 cm spacing) or derived from Rock-Eval 6 (1 m averaging window), has shown the control of orbital forcing on the variation of organic matter distribution. Moreover, and of particular interest, the integration of the Rock Eval Hydrogen Index (HI) and Oxygen Index (OI), providing useful information on the quality of the source rock, were also tested on 164 m long cores from the Lower Vaca Muerta in order to understand the climatic conditions which have favoured the deposition and preservation of organic matter in the basin. In all four signals, cyclic changes were attributed to astronomical forcing. The data shows that the main driver of the slight oxygenation change of the basin is the obliquity. We attribute this link to changes in the sea level due to fluctuations in ice coverage in the ice-house climate of the late Jurassic – early Cretaceous. Moreover, HI, OI and TOC correlate with the precession, the long and the short eccentricity. We thus suggest the following depositional scenario. With falling sea level, the connection between the Neuquén basin and the proto-Pacific gets shallower, resulting in stratification of the basin with warm fresh water supplied from the south of the basin sealing off the deeper basin. With rising sea level, the connection to the ocean gets wider and the stratifications weakens. Nutrients are mainly supplied by continental run-off from the south of the basin due to monsoonal activity during winter, which varies with the precessional cycle. Warm, hypersaline waters are in addition formed in the south-east of the basin, during the parallel formation of the sabkha deposits of the Loma Montosa Formation during summer. This would lead to the formation of a hypersaline lens in the deepest part of the basin and would thus cut it off from oxygen supply.
Complete list of metadatas

https://hal-insu.archives-ouvertes.fr/insu-01718046
Contributor : Isabelle Dubigeon <>
Submitted on : Tuesday, February 27, 2018 - 9:33:31 AM
Last modification on : Friday, August 9, 2019 - 8:22:01 PM

Identifiers

  • HAL Id : insu-01718046, version 1

Collections

Citation

Johannes Monkenbusch, Alain Lejay, Mathieu Martinez, Heiko Pälicke. ORBITAL FORCING OF ORGANIC MATTER QUALITY AND QUANTITY IN A SOURCE-ROCK FORMATION: THE CASE OF THE VACA MUERTA FORMATION, TITHONIAN-VALANGINIAN, NEUQUÉN BASIN, ARGENTINA. International Meeting of Sedimentology 2017, Oct 2017, Toulouse, France. pp.622. ⟨insu-01718046⟩

Share

Metrics

Record views

165