Estudo organofaciológico ao longo do Pliensbaquiano terminal - Toarciano inferior de Rodiles (Astúrias, Espanha).

Abstract

Neste trabalho apresenta-se um estudo de alta resolução estratigráfica da matéria orgânica registada na sucessão margo-calcária do Pliensbaquiano terminal – Toarciano inferior do perfil de Rodiles (Formação de Rodiles, Bacia das Astúrias), suportado na análise geoquímica orgânica (carbono orgânico total (COT) e enxofre (S)) e palinofácies (análise de componentes orgânicos particulados) de 15 amostras de níveis margosos contidos no referido intervalo. Numa série estratigráfica de clara natureza marinha, os resultados obtidos confirmam não só os elevados valores de COT (acima de 2%), já anteriormente referenciados para o limite entre as zonas Tenuicostatum – Serpentium, facto que é acompanhado por um incremento em S (máximo de 3,59%), como evidenciam valores de COT acima de 1% para a Zona Spinatum. O querogénio é dominado em toda a sucessão por fitoclastos, com exceção dos níveis mais ricos em COT, onde existe um claro incremento de matéria orgânica amorfa (MOA). Uma análise mais detalhada desta MOA mostra, à semelhança dos fitoclastos, uma proveniência continental, cuja sedimentação terá sido favorecida por uma diminuição do oxigénio disponível no ambiente deposicional. This work presents a high-resolution stratigraphic study of organic matter recorded in marly-limestone succession of upper Pliensbachian - lower Toarcian from Rodiles section (Rodiles Formation, Asturian Basin), supported by organic geochemistry analysis (total organic carbon (TOC) and sulfur (S)) and palynofacies (analysis of particulate organic compounds) in 15 samples of marly levels. On a stratigraphic series of a clear marine origin, the results confirm not only high values of TOC (above 2 wt.%), previously referenced for the boundary between the Tenuicostatum – Serpentium zones, a fact which is accompanied by an increase in S (maximum of 3.59%), as show for the top of the Spinatum Zone values of TOC above 1%. Across the succession the kerogen is dominated by phytoclasts, with the exception to the richest in TOC levels where there is a clear increase of amorphous organic matter (AOM). A more detailed analysis of this AOM shows, akin to the phytoclasts, a continental provenance, in which sedimentation has been favored by a decrease in the availability of oxygen in the depositional environment.

This work presents a high-resolution stratigraphic study of organic matter recorded in marly-limestone succession of upper Pliensbachian - lower Toarcian from Rodiles section (Rodiles Formation, Asturian Basin), supported by organic geochemistry analysis (total organic carbon (TOC) and sulfur (S)) and palynofacies (analysis of particulate organic compounds) in 15 samples of marly levels. On a stratigraphic series of a clear marine origin, the results confirm not only high values of TOC (above 2 wt.%), previously referenced for the boundary between the Tenuicostatum – Serpentium zones, a fact which is accompanied by an increase in S (maximum of 3.59%), as show for the top of the Spinatum Zone values of TOC above 1%. Across the succession the kerogen is dominated by phytoclasts, with the exception to the richest in TOC levels where there is a clear increase of amorphous organic matter (AOM). A more detailed analysis of this AOM shows, akin to the phytoclasts, a continental provenance, in which sedimentation has been favored by a decrease in the availability of oxygen in the depositional environmen