Presence of charcoal as evidence of paleofires in the Claromecó Basin, Permian of Gondwana, Argentina: Diagenetic and paleoenvironment analysis based on coal petrography studies

CESARETTI, NORA NOEMÍ; ARZADÚN GUADALUPE; TOMEZZOLI, RENATA NELA; CISTERNAS, MARIA EUGENIA

GeoResJ

Elsevier

Año: 2017 vol. 14 p. 121 - 134

2214-2428

The PANG0001 well, situated in the Claromecó Basin, Argentina, involves rocks that belong to the Tunas Formation (Harrington, 1947), Permian of Gondwana. It is composed of fine to medium sandstones intercalate with black and green mudrocks and three coal seams up to 3 m thick. In the coals, a petrographic analysis was carried out to analyze the depositional environment and the diagenesis level reached by the Tunas Formation with the aim of determining its range and its potential as a source rock. The coals are composed of mono-maceral bands of Collotelinite and Gelinite, from the Vitrinite Group, or Fusinite, from the Inertinite Group. They were deposited in a wet swampy forest with rises and decreases of the phreatic level where fires occurred. The vitrinite reflectance values are between 1.3 % and 2.38 %. The coals classify as semiantracitic to low volatile bituminous, with 10 to 25 % of volatile matter. The vitrinite reflectance values indicate the Tunas Formation was buried at 1940 to 2230 m of depth, with temperatures between 140 °C and 190 ºC. The presence of charcoal indicates a paleoclimate change with the presence of paleofires, product of a movement of the Gondwana continent during the Permian. The Tunas Formation reaches the oil to methane gas window, into a catagenesis to metagenesis range related to the organic matter diagenesis. Coal petrography is a good method for the environment and diagenesis analyses applied to the Tunas Formation.