The hydrocarbon source rocks of the Pliensbachian (Early Jurassic) in the Asturian Basin (northern Spain)their relationship with the palaeoclimatic oscillations and gamma-ray response

  1. J. J. Gómez
  2. M. J. Comas-Rengifo
  3. A. Goy
Revista:
Journal of iberian geology: an international publication of earth sciences

ISSN: 1886-7995 1698-6180

Año de publicación: 2016

Volumen: 42

Número: 3

Páginas: 259-273

Tipo: Artículo

DOI: 10.5209/JIGE.53265 DIALNET GOOGLE SCHOLAR lock_openAcceso abierto editor

Otras publicaciones en: Journal of iberian geology: an international publication of earth sciences

Resumen

Normalmente se asume que la sedimentación de las facies de black shales, uno de los principales contribuyentes a la generación de hidro-carburos, está ligada a los Eventos Oceánicos Anóxicos (OAEs) y que éstas facies se formaron durante paleoclimas cálidos. Esta suposición puede orientar a la exploración de rocas madre de hidrocarburos preferentemente hacia los sedimentos depositados bajo paleoambientes cálidos. En consecuencia, el establecimiento de la relación entre paleotemperaturas y la formación de depósitos ricos en materia orgánica resulta de gran importancia para encontrar argumentos sobre este tema, aplicables a la exploración de hidrocarburos. Con este propósito se han estudiado los sedimentos del Sinemuriense Superior, Pliensbachiense y Toarciense Inferior (Jurásico Inferior) de la Cuenca de As-turiana, que incluyen más de 100 m de espesor de depósitos conteniendo facies con materia orgánica y black shales. La correlación entre los datos paleoclimáticos, obtenidos previamente a partir de isótopos de oxígeno, y el contenido de Carbono Orgánico Total (TOC) revela que los black shales y los sedimentos ricos en materia orgánica se depositaron no solo durante los intervalos cálidos sino también durante un destacado evento frío que se desarrolló durante el Pliensbachiense Superior. Este intervalo frío ha sido señalado como uno de los prin-cipales candidatos en los que se podrían haber desarrollado casquetes polares durante el Jurásico. Por el contrario, no se depositaron black shales durante el postulado OAE del Toarciense Inferior, que coincide con un intervalo de supercalentamiento. Además, el estudio de los ciclos de facies y la medida de la radioactividad natural (rayos gamma) en afloramiento, y su correlación con el contenido en TOC, aporta datos sobre el uso de los logs de rayos gamma y los cambios del nivel del mar como proxy para la evaluación preliminar de la riqueza en materia orgánica.

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