Orbital forcing in transgressive/regressive high-frequency sequences (Belsué Syncline, Eocene, South-Pyrenean foreland Basin, Spain).

Abstract

The Belsué syncline crops out in an area of ca. 14 km2 in the southern margin of the Jaca basin (South-Central Pyrenees) which records the transition from marine to non-marine sedimentation over a period of 5.7 Myr during the Eocene (Bartonian-Priabonian). The studied strata are up to 900 m thick and represent a westwards-prograding delta complex, including prodelta (Margas de Arguis formation), delta front (Belsué-Atarés formation) and fluvial beds (Campodarbe formation). These strata were deposited in between two growing anticlines trending perpendicular to the direction of progradation: the Pico del Águila and Gabardiella anticlines. Throughout the syncline a number of transgressive-regressive cycles are governed by Milankovitch eccentricity cycles (Kodama et al., 2010; Garcés et al, 2014). In this work we aim at assessing the mechanisms driving sedimentary cycles by using forward stratigraphic modeling.

To build the model we have used the DIONISOS OpenFlow (Granjeon & Joseph, 1999) to build a reference model of the Belsué syncline, on which different experiments using the available orbital solutions were tested. We explore the nature of changes in the sedimentary record in response to variations in eustacy, sediment supply, and water discharge. These parameters were modulated at different intensities, and tested independently and in different combinations using a Monte-Carlo approach.

The results have been compared with the Belsué outcrops to find the best match with the transgressive-regressive cycles previously defined. In particular, our work is focused on the analysis of the geometry of the different delta front regressive units. In order to evaluate the solutions, a numerical comparison between a representative sedimentary log in the syncline and a virtual log at the same position in the model was carried out, and also a visual comparison of the outcropping section with the virtual equivalent section.