THE RELATIONSHIP BETWEEN SHORELINE TRAJECTORY AND FLUVIAL CHANNEL ARCHITECTURE, NET-SAND CONTENT, CLUSTERING, AND CONNECTIVITY IN A HIGH ACCOMMODATION SETTING, EOCENE ESCANILLA FORMATION, AINSA BASIN, SPAIN

Non-marine sequence stratigraphic models have primarily focused on low accommodation sequences, in which an unconformity is manifested as incised valleys that form during a drop in relative sea level. In comparison, few studies have focused on fluvial strata deposited in a high accommodation setting that produce high accommodation sequences. The Escanilla and Sobrarbe Formations contain world-class outcrops of coevally deposited fluvial-deltaic-deepwater strata in a broadly prograding system. This study uses outcrop data to document how architecture, net-sand content, clustering, and connectivity of fluvial channels relate to changes in shoreline trajectory within a single high accommodation, progradational-retrogradational cycle.

Data from stratigraphic columns, interpreted photopanels, and geologic maps of depositional facies and sand body locations are used to document spatially varying characteristics including, lithology, grain size, sedimentary structures, lithofacies, architectural elements, net-sand content, stratal boundaries, and clustering and connectivity of channel bodies. These data are used to construct longitudinal and lateral cross sections that document the location of the paleoshoreline, regressive and transgressive intervals, and distribution of floodplain deposits and channel bodies, changes in net-sand content, and the location of clustered channels. The regressive interval contains a river-dominated, shelf-margin delta complex that correlates to low aspect-ratio fluvial channel belts, splays and multicolored mudstone sheets. The delta longitudinally correlates to deepwater channels and lobes. In contrast, the transgressive interval is a mixed river-wave-tide-influenced shelf-delta complex with elongate mouth bars that correlates to high aspect-ratio fluvial channel belts, splays, and multicolored mudstone sheets. There are no deepwater deposits located in this interval.

This study documents how the stratigraphic architecture of fluvial channels and floodplains vary in relation to shoreline trajectory in a high accommodation setting in order to improve our understanding of spatial variations in fluvial hydrocarbon reservoir architecture and quality.