CARMINATTI, MARIO, Petrobras, Rio de Janeiro, Brazil; and * GIULIANA VILLA, Istituto di Geologia, Universita di Parma, Italy

ABSTRACT: High Resolution Stratigraphy of the Ilerdian Figols Allogroup (South Pyrenees, Spain)

The 1200 meter thick Figols Allogroup (Ilerdian, southern Pyrenees, Spain), bounded by two regional unconformities and outcropping along a 25 km stretch, offers an unique opportunity to study high frequency cyclicity in the sedimentary record.

The interpretation of the Figols Allogroup is based on measurement of 19 stratigraphic sections for a total thickness of 22 km. We have recognized variations in vertical and lateral facies associations making it possible to frame the stratigraphy in terms of depositional sequences.Eleven stratigraphic units, bounded by unconformities and their correlative conformities, have been recognized; other lesser order units within them were also detected. The eleven units range in thickness from 15 to 300 meters and they represent informal chronostratigraphic subdivisions of the Figols Allogroup. We have generated an acoustic impedence field model to reproduce the sequence boundaries in the study area.

We have also constructed an inverse seismic model of the geological cross section in which acoustic features correspond to each sequence-unit characterized by specific facies associations.

A preliminary study of calcareous nannofossils has been carried out on a part of the study area. The Figols Allogroup consists of CP9 and CP10 Biozones. The boundary between these zones is marked by the first appearance of Discoaster Iodoensis, which is common in the upper part of the Figols. Thus biostratigraphic analyses shows that the time interval of the Figols Allogroup deposition is about 2.7 m.y. However it is still not possible to resolve the time units of each sequence below the 3rd order (1-10 m.y.), because biostratigraphic resolution is not as detailed as that of sequence stratigraphic resolution down to the 4th (0.1-1 m.y.) and probably the 5th (0.01-0.1 m.y.) order cycles achieved in this study.

AAPG Search and Discovery Article #90987©1993 AAPG Annual Convention, New Orleans, Louisiana, April 25-28, 1993.