Estratigrafía del Grupo Fígols (Paleógeno, Cuenca de Graus-Tremp, NE de España)

Zusammenfassung

A litho, bio and cronostratigraphic subdivision of the Ilerdian stratotype in the Graus-Tremp basin is proposed. The Fígols Group comprises a succession of shallow-matine sediments about 750 m in thickness. This succession is characterized by a predominance of marls towards the basin-depocenter and by the development of five carbonate bodies in the southern marginal areas. The Fígols Group includes three formations and nine members. It was deposited between 55.7 Ma and 52.5 Ma, contemporaneously to the Montsec thrust sheet emplacement. As a consequence, several stratigraphic uncomfornities have been recognized. These coincide with the boundaries of bio-chronostratigraphic units. The lower part of the Tendrui marls Formation and the first meters of the La Guardia de Noguera limestone Member correspond to the Lower Ilerdian 1 or biozone SB5. The rest of the La Guardia de Noguera Member and part of the Tendrui F01mation, up to the base of the Esto1m limestone Member are located in the Lower Ilerdian 2 or biozone SB6. From the base of the Estorm Member to the top of the Alsina limestone Member, the Tendrui marls correspond to the Middle Ilerdian 1 or biozone SB7. From the top of the Alsina Member to the top of the marls and the litharenitic sandstones of the Puigverd Formation, the Middle Ilerdian 2 or biozone SB8 is represented. Finally, the Upper Ilerdian or biozone SB9 extends from the base to the top of the mudstones and arkosic sandstones of the Porredó Formation. The Fígols Group is characterized by a vertical evolution showing the superposition of carbonatic, litharenitic and arkosic materials which coincide with the three defined formations. Every formation is characterized by specific sedimentary environments, paleocurrent directions and paleogeographic significance. Moreover, the carbonatic and litharenitic sediments entered the basin from the northeastern margin whereas the arkosic sediments show a clear northern provenance.