Late Oligocene - Early Miocene syntectonic fluvial sedimentation in the Aragonese Pyrenean domain of the Ebro Basin: facies models and structural controls.

Abstract

This contribution deals with a part of the northern margin of the Ebro Basin (Fig. 1). The Upper Oligocene-Lower Miocene molassic infilling in that part mainly corresponds to an extensive fluvial system: the Luna system, which drained the Gavamie unit area and emerged in the basin to the west of the Sierras Exteriores Aragonesas. Small, margina] alluvial fans originated along the Sierras combined in the Luna fluvial system, as well as in the eastern Huesca fluvial system, outside the study area. TIn-ce tectosedimentary units (T.S.U.> were differentiated in the Uncastilio Formation (Figs. 2, 3 and 4), the evolution of whichwas controlled by teetonies affecting the drainage basins. The study of the different lithofacies, their lateral relationsbips and their areal distribution through time (Fig. 5) led to establish sedimentary models for the marginal fans and Luna fluvial system (Hg. 6>. The Luna system resulted from coalescence of two fluvial fans (Figs. 6 and 7). Despite the fluvial network appears mainily as radial, it was controlled by the syndepositional development of the Fuencalderas and Uncastillo anticlines, within the Ebro Basin. Syndepositional folding is shown by important thickness variations in T.S.U., as wel] as by tibe formation of wedge systems within the basin. Progressive uplift of these structures channeled part of the diseharge parallel to tibe basin margin (Figs. 6 and 7), while another portion flowed basinward from the periclinal ends. Vertical aceretion in the synclinal areas north of the anticlines compensated tibe anticlinal uplift, making the siope more genfle and originating bench terraces within tibe general fan slope. In these arcas of gentle slope meandering sandy rivers developed in proximal scctors of tibe systcm, 5.5 lun fair from the margin at present. i